/* SPDX-License-Identifier: GPL-2.0
 *
 * IO cost model based controller.
 *
 * Copyright (C) 2019 Tejun Heo <tj@kernel.org>
 * Copyright (C) 2019 Andy Newell <newella@fb.com>
 * Copyright (C) 2019 Facebook
 *
 * One challenge of controlling IO resources is the lack of trivially
 * observable cost metric.  This is distinguished from CPU and memory where
 * wallclock time and the number of bytes can serve as accurate enough
 * approximations.
 *
 * Bandwidth and iops are the most commonly used metrics for IO devices but
 * depending on the type and specifics of the device, different IO patterns
 * easily lead to multiple orders of magnitude variations rendering them
 * useless for the purpose of IO capacity distribution.  While on-device
 * time, with a lot of clutches, could serve as a useful approximation for
 * non-queued rotational devices, this is no longer viable with modern
 * devices, even the rotational ones.
 *
 * While there is no cost metric we can trivially observe, it isn't a
 * complete mystery.  For example, on a rotational device, seek cost
 * dominates while a contiguous transfer contributes a smaller amount
 * proportional to the size.  If we can characterize at least the relative
 * costs of these different types of IOs, it should be possible to
 * implement a reasonable work-conserving proportional IO resource
 * distribution.
 *
 * 1. IO Cost Model
 *
 * IO cost model estimates the cost of an IO given its basic parameters and
 * history (e.g. the end sector of the last IO).  The cost is measured in
 * device time.  If a given IO is estimated to cost 10ms, the device should
 * be able to process ~100 of those IOs in a second.
 *
 * Currently, there's only one builtin cost model - linear.  Each IO is
 * classified as sequential or random and given a base cost accordingly.
 * On top of that, a size cost proportional to the length of the IO is
 * added.  While simple, this model captures the operational
 * characteristics of a wide varienty of devices well enough.  Default
 * parameters for several different classes of devices are provided and the
 * parameters can be configured from userspace via
 * /sys/fs/cgroup/io.cost.model.
 *
 * If needed, tools/cgroup/iocost_coef_gen.py can be used to generate
 * device-specific coefficients.
 *
 * 2. Control Strategy
 *
 * The device virtual time (vtime) is used as the primary control metric.
 * The control strategy is composed of the following three parts.
 *
 * 2-1. Vtime Distribution
 *
 * When a cgroup becomes active in terms of IOs, its hierarchical share is
 * calculated.  Please consider the following hierarchy where the numbers
 * inside parentheses denote the configured weights.
 *
 *           root
 *         /       \
 *      A (w:100)  B (w:300)
 *      /       \
 *  A0 (w:100)  A1 (w:100)
 *
 * If B is idle and only A0 and A1 are actively issuing IOs, as the two are
 * of equal weight, each gets 50% share.  If then B starts issuing IOs, B
 * gets 300/(100+300) or 75% share, and A0 and A1 equally splits the rest,
 * 12.5% each.  The distribution mechanism only cares about these flattened
 * shares.  They're called hweights (hierarchical weights) and always add
 * upto 1 (WEIGHT_ONE).
 *
 * A given cgroup's vtime runs slower in inverse proportion to its hweight.
 * For example, with 12.5% weight, A0's time runs 8 times slower (100/12.5)
 * against the device vtime - an IO which takes 10ms on the underlying
 * device is considered to take 80ms on A0.
 *
 * This constitutes the basis of IO capacity distribution.  Each cgroup's
 * vtime is running at a rate determined by its hweight.  A cgroup tracks
 * the vtime consumed by past IOs and can issue a new IO if doing so
 * wouldn't outrun the current device vtime.  Otherwise, the IO is
 * suspended until the vtime has progressed enough to cover it.
 *
 * 2-2. Vrate Adjustment
 *
 * It's unrealistic to expect the cost model to be perfect.  There are too
 * many devices and even on the same device the overall performance
 * fluctuates depending on numerous factors such as IO mixture and device
 * internal garbage collection.  The controller needs to adapt dynamically.
 *
 * This is achieved by adjusting the overall IO rate according to how busy
 * the device is.  If the device becomes overloaded, we're sending down too
 * many IOs and should generally slow down.  If there are waiting issuers
 * but the device isn't saturated, we're issuing too few and should
 * generally speed up.
 *
 * To slow down, we lower the vrate - the rate at which the device vtime
 * passes compared to the wall clock.  For example, if the vtime is running
 * at the vrate of 75%, all cgroups added up would only be able to issue
 * 750ms worth of IOs per second, and vice-versa for speeding up.
 *
 * Device business is determined using two criteria - rq wait and
 * completion latencies.
 *
 * When a device gets saturated, the on-device and then the request queues
 * fill up and a bio which is ready to be issued has to wait for a request
 * to become available.  When this delay becomes noticeable, it's a clear
 * indication that the device is saturated and we lower the vrate.  This
 * saturation signal is fairly conservative as it only triggers when both
 * hardware and software queues are filled up, and is used as the default
 * busy signal.
 *
 * As devices can have deep queues and be unfair in how the queued commands
 * are executed, soley depending on rq wait may not result in satisfactory
 * control quality.  For a better control quality, completion latency QoS
 * parameters can be configured so that the device is considered saturated
 * if N'th percentile completion latency rises above the set point.
 *
 * The completion latency requirements are a function of both the
 * underlying device characteristics and the desired IO latency quality of
 * service.  There is an inherent trade-off - the tighter the latency QoS,
 * the higher the bandwidth lossage.  Latency QoS is disabled by default
 * and can be set through /sys/fs/cgroup/io.cost.qos.
 *
 * 2-3. Work Conservation
 *
 * Imagine two cgroups A and B with equal weights.  A is issuing a small IO
 * periodically while B is sending out enough parallel IOs to saturate the
 * device on its own.  Let's say A's usage amounts to 100ms worth of IO
 * cost per second, i.e., 10% of the device capacity.  The naive
 * distribution of half and half would lead to 60% utilization of the
 * device, a significant reduction in the total amount of work done
 * compared to free-for-all competition.  This is too high a cost to pay
 * for IO control.
 *
 * To conserve the total amount of work done, we keep track of how much
 * each active cgroup is actually using and yield part of its weight if
 * there are other cgroups which can make use of it.  In the above case,
 * A's weight will be lowered so that it hovers above the actual usage and
 * B would be able to use the rest.
 *
 * As we don't want to penalize a cgroup for donating its weight, the
 * surplus weight adjustment factors in a margin and has an immediate
 * snapback mechanism in case the cgroup needs more IO vtime for itself.
 *
 * Note that adjusting down surplus weights has the same effects as
 * accelerating vtime for other cgroups and work conservation can also be
 * implemented by adjusting vrate dynamically.  However, squaring who can
 * donate and should take back how much requires hweight propagations
 * anyway making it easier to implement and understand as a separate
 * mechanism.
 *
 * 3. Monitoring
 *
 * Instead of debugfs or other clumsy monitoring mechanisms, this
 * controller uses a drgn based monitoring script -
 * tools/cgroup/iocost_monitor.py.  For details on drgn, please see
 * https://github.com/osandov/drgn.  The output looks like the following.
 *
 *  sdb RUN   per=300ms cur_per=234.218:v203.695 busy= +1 vrate= 62.12%
 *                 active      weight      hweight% inflt% dbt  delay usages%
 *  test/a              *    50/   50  33.33/ 33.33  27.65   2  0*041 033:033:033
 *  test/b              *   100/  100  66.67/ 66.67  17.56   0  0*000 066:079:077
 *
 * - per        : Timer period
 * - cur_per    : Internal wall and device vtime clock
 * - vrate      : Device virtual time rate against wall clock
 * - weight     : Surplus-adjusted and configured weights
 * - hweight    : Surplus-adjusted and configured hierarchical weights
 * - inflt      : The percentage of in-flight IO cost at the end of last period
 * - del_ms     : Deferred issuer delay induction level and duration
 * - usages     : Usage history
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/timer.h>
#include <linux/time64.h>
#include <linux/parser.h>
#include <linux/sched/signal.h>
#include <linux/blk-cgroup.h>
#include <asm/local.h>
#include <asm/local64.h>
#include "blk-rq-qos.h"
#include "blk-stat.h"
#include "blk-wbt.h"

#ifdef CONFIG_TRACEPOINTS

/* copied from TRACE_CGROUP_PATH, see cgroup-internal.h */
#define TRACE_IOCG_PATH_LEN 1024
static DEFINE_SPINLOCK(trace_iocg_path_lock);
static char trace_iocg_path[TRACE_IOCG_PATH_LEN];

#define TRACE_IOCG_PATH(type, iocg, ...)                                        \
        do {                                                                    \
                unsigned long flags;                                            \
                if (trace_iocost_##type##_enabled()) {                          \
                        spin_lock_irqsave(&trace_iocg_path_lock, flags);        \
                        cgroup_path(iocg_to_blkg(iocg)->blkcg->css.cgroup,      \
                                    trace_iocg_path, TRACE_IOCG_PATH_LEN);      \
                        trace_iocost_##type(iocg, trace_iocg_path,              \
                                              ##__VA_ARGS__);                   \
                        spin_unlock_irqrestore(&trace_iocg_path_lock, flags);   \
                }                                                               \
        } while (0)

#else   /* CONFIG_TRACE_POINTS */
#define TRACE_IOCG_PATH(type, iocg, ...)        do { } while (0)
#endif  /* CONFIG_TRACE_POINTS */

enum {
        MILLION                 = 1000000,

        /* timer period is calculated from latency requirements, bound it */
        MIN_PERIOD              = USEC_PER_MSEC,
        MAX_PERIOD              = USEC_PER_SEC,

        /*
         * iocg->vtime is targeted at 50% behind the device vtime, which
         * serves as its IO credit buffer.  Surplus weight adjustment is
         * immediately canceled if the vtime margin runs below 10%.
         */
        MARGIN_MIN_PCT          = 10,
        MARGIN_LOW_PCT          = 20,
        MARGIN_TARGET_PCT       = 50,

        INUSE_ADJ_STEP_PCT      = 25,

        /* Have some play in timer operations */
        TIMER_SLACK_PCT         = 1,

        /* 1/64k is granular enough and can easily be handled w/ u32 */
        WEIGHT_ONE              = 1 << 16,

        /*
         * As vtime is used to calculate the cost of each IO, it needs to
         * be fairly high precision.  For example, it should be able to
         * represent the cost of a single page worth of discard with
         * suffificient accuracy.  At the same time, it should be able to
         * represent reasonably long enough durations to be useful and
         * convenient during operation.
         *
         * 1s worth of vtime is 2^37.  This gives us both sub-nanosecond
         * granularity and days of wrap-around time even at extreme vrates.
         */
        VTIME_PER_SEC_SHIFT     = 37,
        VTIME_PER_SEC           = 1LLU << VTIME_PER_SEC_SHIFT,
        VTIME_PER_USEC          = VTIME_PER_SEC / USEC_PER_SEC,
        VTIME_PER_NSEC          = VTIME_PER_SEC / NSEC_PER_SEC,

        /* bound vrate adjustments within two orders of magnitude */
        VRATE_MIN_PPM           = 10000,        /* 1% */
        VRATE_MAX_PPM           = 100000000,    /* 10000% */

        VRATE_MIN               = VTIME_PER_USEC * VRATE_MIN_PPM / MILLION,
        VRATE_CLAMP_ADJ_PCT     = 4,

        /* if IOs end up waiting for requests, issue less */
        RQ_WAIT_BUSY_PCT        = 5,

        /* unbusy hysterisis */
        UNBUSY_THR_PCT          = 75,

        /*
         * The effect of delay is indirect and non-linear and a huge amount of
         * future debt can accumulate abruptly while unthrottled. Linearly scale
         * up delay as debt is going up and then let it decay exponentially.
         * This gives us quick ramp ups while delay is accumulating and long
         * tails which can help reducing the frequency of debt explosions on
         * unthrottle. The parameters are experimentally determined.
         *
         * The delay mechanism provides adequate protection and behavior in many
         * cases. However, this is far from ideal and falls shorts on both
         * fronts. The debtors are often throttled too harshly costing a
         * significant level of fairness and possibly total work while the
         * protection against their impacts on the system can be choppy and
         * unreliable.
         *
         * The shortcoming primarily stems from the fact that, unlike for page
         * cache, the kernel doesn't have well-defined back-pressure propagation
         * mechanism and policies for anonymous memory. Fully addressing this
         * issue will likely require substantial improvements in the area.
         */
        MIN_DELAY_THR_PCT       = 500,
        MAX_DELAY_THR_PCT       = 25000,
        MIN_DELAY               = 250,
        MAX_DELAY               = 250 * USEC_PER_MSEC,

        /* halve debts if avg usage over 100ms is under 50% */
        DFGV_USAGE_PCT          = 50,
        DFGV_PERIOD             = 100 * USEC_PER_MSEC,

        /* don't let cmds which take a very long time pin lagging for too long */
        MAX_LAGGING_PERIODS     = 10,

        /* switch iff the conditions are met for longer than this */
        AUTOP_CYCLE_NSEC        = 10LLU * NSEC_PER_SEC,

        /*
         * Count IO size in 4k pages.  The 12bit shift helps keeping
         * size-proportional components of cost calculation in closer
         * numbers of digits to per-IO cost components.
         */
        IOC_PAGE_SHIFT          = 12,
        IOC_PAGE_SIZE           = 1 << IOC_PAGE_SHIFT,
        IOC_SECT_TO_PAGE_SHIFT  = IOC_PAGE_SHIFT - SECTOR_SHIFT,

        /* if apart further than 16M, consider randio for linear model */
        LCOEF_RANDIO_PAGES      = 4096,
};

enum ioc_running {
        IOC_IDLE,
        IOC_RUNNING,
        IOC_STOP,
};

/* io.cost.qos controls including per-dev enable of the whole controller */
enum {
        QOS_ENABLE,
        QOS_CTRL,
        NR_QOS_CTRL_PARAMS,
};

/* io.cost.qos params */
enum {
        QOS_RPPM,
        QOS_RLAT,
        QOS_WPPM,
        QOS_WLAT,
        QOS_MIN,
        QOS_MAX,
        NR_QOS_PARAMS,
};

/* io.cost.model controls */
enum {
        COST_CTRL,
        COST_MODEL,
        NR_COST_CTRL_PARAMS,
};

/* builtin linear cost model coefficients */
enum {
        I_LCOEF_RBPS,
        I_LCOEF_RSEQIOPS,
        I_LCOEF_RRANDIOPS,
        I_LCOEF_WBPS,
        I_LCOEF_WSEQIOPS,
        I_LCOEF_WRANDIOPS,
        NR_I_LCOEFS,
};

enum {
        LCOEF_RPAGE,
        LCOEF_RSEQIO,
        LCOEF_RRANDIO,
        LCOEF_WPAGE,
        LCOEF_WSEQIO,
        LCOEF_WRANDIO,
        NR_LCOEFS,
};

enum {
        AUTOP_INVALID,
        AUTOP_HDD,
        AUTOP_SSD_QD1,
        AUTOP_SSD_DFL,
        AUTOP_SSD_FAST,
};

struct ioc_params {
        u32                             qos[NR_QOS_PARAMS];
        u64                             i_lcoefs[NR_I_LCOEFS];
        u64                             lcoefs[NR_LCOEFS];
        u32                             too_fast_vrate_pct;
        u32                             too_slow_vrate_pct;
};

struct ioc_margins {
        s64                             min;
        s64                             low;
        s64                             target;
};

struct ioc_missed {
        local_t                         nr_met;
        local_t                         nr_missed;
        u32                             last_met;
        u32                             last_missed;
};

struct ioc_pcpu_stat {
        struct ioc_missed               missed[2];

        local64_t                       rq_wait_ns;
        u64                             last_rq_wait_ns;
};

/* per device */
struct ioc {
        struct rq_qos                   rqos;

        bool                            enabled;

        struct ioc_params               params;
        struct ioc_margins              margins;
        u32                             period_us;
        u32                             timer_slack_ns;
        u64                             vrate_min;
        u64                             vrate_max;

        spinlock_t                      lock;
        struct timer_list               timer;
        struct list_head                active_iocgs;   /* active cgroups */
        struct ioc_pcpu_stat __percpu   *pcpu_stat;

        enum ioc_running                running;
        atomic64_t                      vtime_rate;
        u64                             vtime_base_rate;
        s64                             vtime_err;

        seqcount_spinlock_t             period_seqcount;
        u64                             period_at;      /* wallclock starttime */
        u64                             period_at_vtime; /* vtime starttime */

        atomic64_t                      cur_period;     /* inc'd each period */
        int                             busy_level;     /* saturation history */

        bool                            weights_updated;
        atomic_t                        hweight_gen;    /* for lazy hweights */

        /* debt forgivness */
        u64                             dfgv_period_at;
        u64                             dfgv_period_rem;
        u64                             dfgv_usage_us_sum;

        u64                             autop_too_fast_at;
        u64                             autop_too_slow_at;
        int                             autop_idx;
        bool                            user_qos_params:1;
        bool                            user_cost_model:1;
};

struct iocg_pcpu_stat {
        local64_t                       abs_vusage;
};

struct iocg_stat {
        u64                             usage_us;
        u64                             wait_us;
        u64                             indebt_us;
        u64                             indelay_us;
};

/* per device-cgroup pair */
struct ioc_gq {
        struct blkg_policy_data         pd;
        struct ioc                      *ioc;

        /*
         * A iocg can get its weight from two sources - an explicit
         * per-device-cgroup configuration or the default weight of the
         * cgroup.  `cfg_weight` is the explicit per-device-cgroup
         * configuration.  `weight` is the effective considering both
         * sources.
         *
         * When an idle cgroup becomes active its `active` goes from 0 to
         * `weight`.  `inuse` is the surplus adjusted active weight.
         * `active` and `inuse` are used to calculate `hweight_active` and
         * `hweight_inuse`.
         *
         * `last_inuse` remembers `inuse` while an iocg is idle to persist
         * surplus adjustments.
         *
         * `inuse` may be adjusted dynamically during period. `saved_*` are used
         * to determine and track adjustments.
         */
        u32                             cfg_weight;
        u32                             weight;
        u32                             active;
        u32                             inuse;

        u32                             last_inuse;
        s64                             saved_margin;

        sector_t                        cursor;         /* to detect randio */

        /*
         * `vtime` is this iocg's vtime cursor which progresses as IOs are
         * issued.  If lagging behind device vtime, the delta represents
         * the currently available IO budget.  If running ahead, the
         * overage.
         *
         * `vtime_done` is the same but progressed on completion rather
         * than issue.  The delta behind `vtime` represents the cost of
         * currently in-flight IOs.
         */
        atomic64_t                      vtime;
        atomic64_t                      done_vtime;
        u64                             abs_vdebt;

        /* current delay in effect and when it started */
        u64                             delay;
        u64                             delay_at;

        /*
         * The period this iocg was last active in.  Used for deactivation
         * and invalidating `vtime`.
         */
        atomic64_t                      active_period;
        struct list_head                active_list;

        /* see __propagate_weights() and current_hweight() for details */
        u64                             child_active_sum;
        u64                             child_inuse_sum;
        u64                             child_adjusted_sum;
        int                             hweight_gen;
        u32                             hweight_active;
        u32                             hweight_inuse;
        u32                             hweight_donating;
        u32                             hweight_after_donation;

        struct list_head                walk_list;
        struct list_head                surplus_list;

        struct wait_queue_head          waitq;
        struct hrtimer                  waitq_timer;

        /* timestamp at the latest activation */
        u64                             activated_at;

        /* statistics */
        struct iocg_pcpu_stat __percpu  *pcpu_stat;
        struct iocg_stat                local_stat;
        struct iocg_stat                desc_stat;
        struct iocg_stat                last_stat;
        u64                             last_stat_abs_vusage;
        u64                             usage_delta_us;
        u64                             wait_since;
        u64                             indebt_since;
        u64                             indelay_since;

        /* this iocg's depth in the hierarchy and ancestors including self */
        int                             level;
        struct ioc_gq                   *ancestors[];
};

/* per cgroup */
struct ioc_cgrp {
        struct blkcg_policy_data        cpd;
        unsigned int                    dfl_weight;
};

struct ioc_now {
        u64                             now_ns;
        u64                             now;
        u64                             vnow;
        u64                             vrate;
};

struct iocg_wait {
        struct wait_queue_entry         wait;
        struct bio                      *bio;
        u64                             abs_cost;
        bool                            committed;
};

struct iocg_wake_ctx {
        struct ioc_gq                   *iocg;
        u32                             hw_inuse;
        s64                             vbudget;
};

static const struct ioc_params autop[] = {
        [AUTOP_HDD] = {
                .qos                            = {
                        [QOS_RLAT]              =        250000, /* 250ms */
                        [QOS_WLAT]              =        250000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =     174019176,
                        [I_LCOEF_RSEQIOPS]      =         41708,
                        [I_LCOEF_RRANDIOPS]     =           370,
                        [I_LCOEF_WBPS]          =     178075866,
                        [I_LCOEF_WSEQIOPS]      =         42705,
                        [I_LCOEF_WRANDIOPS]     =           378,
                },
        },
        [AUTOP_SSD_QD1] = {
                .qos                            = {
                        [QOS_RLAT]              =         25000, /* 25ms */
                        [QOS_WLAT]              =         25000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =     245855193,
                        [I_LCOEF_RSEQIOPS]      =         61575,
                        [I_LCOEF_RRANDIOPS]     =          6946,
                        [I_LCOEF_WBPS]          =     141365009,
                        [I_LCOEF_WSEQIOPS]      =         33716,
                        [I_LCOEF_WRANDIOPS]     =         26796,
                },
        },
        [AUTOP_SSD_DFL] = {
                .qos                            = {
                        [QOS_RLAT]              =         25000, /* 25ms */
                        [QOS_WLAT]              =         25000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =     488636629,
                        [I_LCOEF_RSEQIOPS]      =          8932,
                        [I_LCOEF_RRANDIOPS]     =          8518,
                        [I_LCOEF_WBPS]          =     427891549,
                        [I_LCOEF_WSEQIOPS]      =         28755,
                        [I_LCOEF_WRANDIOPS]     =         21940,
                },
                .too_fast_vrate_pct             =           500,
        },
        [AUTOP_SSD_FAST] = {
                .qos                            = {
                        [QOS_RLAT]              =          5000, /* 5ms */
                        [QOS_WLAT]              =          5000,
                        [QOS_MIN]               = VRATE_MIN_PPM,
                        [QOS_MAX]               = VRATE_MAX_PPM,
                },
                .i_lcoefs                       = {
                        [I_LCOEF_RBPS]          =    3102524156LLU,
                        [I_LCOEF_RSEQIOPS]      =        724816,
                        [I_LCOEF_RRANDIOPS]     =        778122,
                        [I_LCOEF_WBPS]          =    1742780862LLU,
                        [I_LCOEF_WSEQIOPS]      =        425702,
                        [I_LCOEF_WRANDIOPS]     =        443193,
                },
                .too_slow_vrate_pct             =            10,
        },
};

/*
 * vrate adjust percentages indexed by ioc->busy_level.  We adjust up on
 * vtime credit shortage and down on device saturation.
 */
static u32 vrate_adj_pct[] =
        { 0, 0, 0, 0,
          1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
          2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
          4, 4, 4, 4, 4, 4, 4, 4, 8, 8, 8, 8, 8, 8, 8, 8, 16 };

static struct blkcg_policy blkcg_policy_iocost;

/* accessors and helpers */
static struct ioc *rqos_to_ioc(struct rq_qos *rqos)
{
        return container_of(rqos, struct ioc, rqos);
}

static struct ioc *q_to_ioc(struct request_queue *q)
{
        return rqos_to_ioc(rq_qos_id(q, RQ_QOS_COST));
}

static const char *q_name(struct request_queue *q)
{
        if (blk_queue_registered(q))
                return kobject_name(q->kobj.parent);
        else
                return "<unknown>";
}

static const char __maybe_unused *ioc_name(struct ioc *ioc)
{
        return q_name(ioc->rqos.q);
}

static struct ioc_gq *pd_to_iocg(struct blkg_policy_data *pd)
{
        return pd ? container_of(pd, struct ioc_gq, pd) : NULL;
}

static struct ioc_gq *blkg_to_iocg(struct blkcg_gq *blkg)
{
        return pd_to_iocg(blkg_to_pd(blkg, &blkcg_policy_iocost));
}

static struct blkcg_gq *iocg_to_blkg(struct ioc_gq *iocg)
{
        return pd_to_blkg(&iocg->pd);
}

static struct ioc_cgrp *blkcg_to_iocc(struct blkcg *blkcg)
{
        return container_of(blkcg_to_cpd(blkcg, &blkcg_policy_iocost),
                            struct ioc_cgrp, cpd);
}

/*
 * Scale @abs_cost to the inverse of @hw_inuse.  The lower the hierarchical
 * weight, the more expensive each IO.  Must round up.
 */
static u64 abs_cost_to_cost(u64 abs_cost, u32 hw_inuse)
{
        return DIV64_U64_ROUND_UP(abs_cost * WEIGHT_ONE, hw_inuse);
}

/*
 * The inverse of abs_cost_to_cost().  Must round up.
 */
static u64 cost_to_abs_cost(u64 cost, u32 hw_inuse)
{
        return DIV64_U64_ROUND_UP(cost * hw_inuse, WEIGHT_ONE);
}

static void iocg_commit_bio(struct ioc_gq *iocg, struct bio *bio,
                            u64 abs_cost, u64 cost)
{
        struct iocg_pcpu_stat *gcs;

        bio->bi_iocost_cost = cost;
        atomic64_add(cost, &iocg->vtime);

        gcs = get_cpu_ptr(iocg->pcpu_stat);
        local64_add(abs_cost, &gcs->abs_vusage);
        put_cpu_ptr(gcs);
}

static void iocg_lock(struct ioc_gq *iocg, bool lock_ioc, unsigned long *flags)
{
        if (lock_ioc) {
                spin_lock_irqsave(&iocg->ioc->lock, *flags);
                spin_lock(&iocg->waitq.lock);
        } else {
                spin_lock_irqsave(&iocg->waitq.lock, *flags);
        }
}

static void iocg_unlock(struct ioc_gq *iocg, bool unlock_ioc, unsigned long *flags)
{
        if (unlock_ioc) {
                spin_unlock(&iocg->waitq.lock);
                spin_unlock_irqrestore(&iocg->ioc->lock, *flags);
        } else {
                spin_unlock_irqrestore(&iocg->waitq.lock, *flags);
        }
}

#define CREATE_TRACE_POINTS
#include <trace/events/iocost.h>

static void ioc_refresh_margins(struct ioc *ioc)
{
        struct ioc_margins *margins = &ioc->margins;
        u32 period_us = ioc->period_us;
        u64 vrate = ioc->vtime_base_rate;

        margins->min = (period_us * MARGIN_MIN_PCT / 100) * vrate;
        margins->low = (period_us * MARGIN_LOW_PCT / 100) * vrate;
        margins->target = (period_us * MARGIN_TARGET_PCT / 100) * vrate;
}

/* latency Qos params changed, update period_us and all the dependent params */
static void ioc_refresh_period_us(struct ioc *ioc)
{
        u32 ppm, lat, multi, period_us;

        lockdep_assert_held(&ioc->lock);

        /* pick the higher latency target */
        if (ioc->params.qos[QOS_RLAT] >= ioc->params.qos[QOS_WLAT]) {
                ppm = ioc->params.qos[QOS_RPPM];
                lat = ioc->params.qos[QOS_RLAT];
        } else {
                ppm = ioc->params.qos[QOS_WPPM];
                lat = ioc->params.qos[QOS_WLAT];
        }

        /*
         * We want the period to be long enough to contain a healthy number
         * of IOs while short enough for granular control.  Define it as a
         * multiple of the latency target.  Ideally, the multiplier should
         * be scaled according to the percentile so that it would nominally
         * contain a certain number of requests.  Let's be simpler and
         * scale it linearly so that it's 2x >= pct(90) and 10x at pct(50).
         */
        if (ppm)
                multi = max_t(u32, (MILLION - ppm) / 50000, 2);
        else
                multi = 2;
        period_us = multi * lat;
        period_us = clamp_t(u32, period_us, MIN_PERIOD, MAX_PERIOD);

        /* calculate dependent params */
        ioc->period_us = period_us;
        ioc->timer_slack_ns = div64_u64(
                (u64)period_us * NSEC_PER_USEC * TIMER_SLACK_PCT,
                100);
        ioc_refresh_margins(ioc);
}

static int ioc_autop_idx(struct ioc *ioc)
{
        int idx = ioc->autop_idx;
        const struct ioc_params *p = &autop[idx];
        u32 vrate_pct;
        u64 now_ns;

        /* rotational? */
        if (!blk_queue_nonrot(ioc->rqos.q))
                return AUTOP_HDD;

        /* handle SATA SSDs w/ broken NCQ */
        if (blk_queue_depth(ioc->rqos.q) == 1)
                return AUTOP_SSD_QD1;

        /* use one of the normal ssd sets */
        if (idx < AUTOP_SSD_DFL)
                return AUTOP_SSD_DFL;

        /* if user is overriding anything, maintain what was there */
        if (ioc->user_qos_params || ioc->user_cost_model)
                return idx;

        /* step up/down based on the vrate */
        vrate_pct = div64_u64(ioc->vtime_base_rate * 100, VTIME_PER_USEC);
        now_ns = ktime_get_ns();

        if (p->too_fast_vrate_pct && p->too_fast_vrate_pct <= vrate_pct) {
                if (!ioc->autop_too_fast_at)
                        ioc->autop_too_fast_at = now_ns;
                if (now_ns - ioc->autop_too_fast_at >= AUTOP_CYCLE_NSEC)
                        return idx + 1;
        } else {
                ioc->autop_too_fast_at = 0;
        }

        if (p->too_slow_vrate_pct && p->too_slow_vrate_pct >= vrate_pct) {
                if (!ioc->autop_too_slow_at)
                        ioc->autop_too_slow_at = now_ns;
                if (now_ns - ioc->autop_too_slow_at >= AUTOP_CYCLE_NSEC)
                        return idx - 1;
        } else {
                ioc->autop_too_slow_at = 0;
        }

        return idx;
}

/*
 * Take the followings as input
 *
 *  @bps        maximum sequential throughput
 *  @seqiops    maximum sequential 4k iops
 *  @randiops   maximum random 4k iops
 *
 * and calculate the linear model cost coefficients.
 *
 *  *@page      per-page cost           1s / (@bps / 4096)
 *  *@seqio     base cost of a seq IO   max((1s / @seqiops) - *@page, 0)
 *  @randiops   base cost of a rand IO  max((1s / @randiops) - *@page, 0)
 */
static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,
                        u64 *page, u64 *seqio, u64 *randio)
{
        u64 v;

        *page = *seqio = *randio = 0;

        if (bps)
                *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
                                           DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));

        if (seqiops) {
                v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, seqiops);
                if (v > *page)
                        *seqio = v - *page;
        }

        if (randiops) {
                v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, randiops);
                if (v > *page)
                        *randio = v - *page;
        }
}

static void ioc_refresh_lcoefs(struct ioc *ioc)
{
        u64 *u = ioc->params.i_lcoefs;
        u64 *c = ioc->params.lcoefs;

        calc_lcoefs(u[I_LCOEF_RBPS], u[I_LCOEF_RSEQIOPS], u[I_LCOEF_RRANDIOPS],
                    &c[LCOEF_RPAGE], &c[LCOEF_RSEQIO], &c[LCOEF_RRANDIO]);
        calc_lcoefs(u[I_LCOEF_WBPS], u[I_LCOEF_WSEQIOPS], u[I_LCOEF_WRANDIOPS],
                    &c[LCOEF_WPAGE], &c[LCOEF_WSEQIO], &c[LCOEF_WRANDIO]);
}

static bool ioc_refresh_params(struct ioc *ioc, bool force)
{
        const struct ioc_params *p;
        int idx;

        lockdep_assert_held(&ioc->lock);

        idx = ioc_autop_idx(ioc);
        p = &autop[idx];

        if (idx == ioc->autop_idx && !force)
                return false;

        if (idx != ioc->autop_idx)
                atomic64_set(&ioc->vtime_rate, VTIME_PER_USEC);

        ioc->autop_idx = idx;
        ioc->autop_too_fast_at = 0;
        ioc->autop_too_slow_at = 0;

        if (!ioc->user_qos_params)
                memcpy(ioc->params.qos, p->qos, sizeof(p->qos));
        if (!ioc->user_cost_model)
                memcpy(ioc->params.i_lcoefs, p->i_lcoefs, sizeof(p->i_lcoefs));

        ioc_refresh_period_us(ioc);
        ioc_refresh_lcoefs(ioc);

        ioc->vrate_min = DIV64_U64_ROUND_UP((u64)ioc->params.qos[QOS_MIN] *
                                            VTIME_PER_USEC, MILLION);
        ioc->vrate_max = div64_u64((u64)ioc->params.qos[QOS_MAX] *
                                   VTIME_PER_USEC, MILLION);

        return true;
}

/*
 * When an iocg accumulates too much vtime or gets deactivated, we throw away
 * some vtime, which lowers the overall device utilization. As the exact amount
 * which is being thrown away is known, we can compensate by accelerating the
 * vrate accordingly so that the extra vtime generated in the current period
 * matches what got lost.
 */
static void ioc_refresh_vrate(struct ioc *ioc, struct ioc_now *now)
{
        s64 pleft = ioc->period_at + ioc->period_us - now->now;
        s64 vperiod = ioc->period_us * ioc->vtime_base_rate;
        s64 vcomp, vcomp_min, vcomp_max;

        lockdep_assert_held(&ioc->lock);

        /* we need some time left in this period */
        if (pleft <= 0)
                goto done;

        /*
         * Calculate how much vrate should be adjusted to offset the error.
         * Limit the amount of adjustment and deduct the adjusted amount from
         * the error.
         */
        vcomp = -div64_s64(ioc->vtime_err, pleft);
        vcomp_min = -(ioc->vtime_base_rate >> 1);
        vcomp_max = ioc->vtime_base_rate;
        vcomp = clamp(vcomp, vcomp_min, vcomp_max);

        ioc->vtime_err += vcomp * pleft;

        atomic64_set(&ioc->vtime_rate, ioc->vtime_base_rate + vcomp);
done:
        /* bound how much error can accumulate */
        ioc->vtime_err = clamp(ioc->vtime_err, -vperiod, vperiod);
}

static void ioc_adjust_base_vrate(struct ioc *ioc, u32 rq_wait_pct,
                                  int nr_lagging, int nr_shortages,
                                  int prev_busy_level, u32 *missed_ppm)
{
        u64 vrate = ioc->vtime_base_rate;
        u64 vrate_min = ioc->vrate_min, vrate_max = ioc->vrate_max;

        if (!ioc->busy_level || (ioc->busy_level < 0 && nr_lagging)) {
                if (ioc->busy_level != prev_busy_level || nr_lagging)
                        trace_iocost_ioc_vrate_adj(ioc, atomic64_read(&ioc->vtime_rate),
                                                   missed_ppm, rq_wait_pct,
                                                   nr_lagging, nr_shortages);

                return;
        }

        /*
         * If vrate is out of bounds, apply clamp gradually as the
         * bounds can change abruptly.  Otherwise, apply busy_level
         * based adjustment.
         */
        if (vrate < vrate_min) {
                vrate = div64_u64(vrate * (100 + VRATE_CLAMP_ADJ_PCT), 100);
                vrate = min(vrate, vrate_min);
        } else if (vrate > vrate_max) {
                vrate = div64_u64(vrate * (100 - VRATE_CLAMP_ADJ_PCT), 100);
                vrate = max(vrate, vrate_max);

        } else {
                int idx = min_t(int, abs(ioc->busy_level),
                                ARRAY_SIZE(vrate_adj_pct) - 1);
                u32 adj_pct = vrate_adj_pct[idx];

                if (ioc->busy_level > 0)
                        adj_pct = 100 - adj_pct;
                else
                        adj_pct = 100 + adj_pct;

                vrate = clamp(DIV64_U64_ROUND_UP(vrate * adj_pct, 100),
                              vrate_min, vrate_max);
        }

        trace_iocost_ioc_vrate_adj(ioc, vrate, missed_ppm, rq_wait_pct,
                                   nr_lagging, nr_shortages);

        ioc->vtime_base_rate = vrate;
        ioc_refresh_margins(ioc);
}

/* take a snapshot of the current [v]time and vrate */
static void ioc_now(struct ioc *ioc, struct ioc_now *now)
{
        unsigned seq;

        now->now_ns = ktime_get();
        now->now = ktime_to_us(now->now_ns);
        now->vrate = atomic64_read(&ioc->vtime_rate);

        /*
         * The current vtime is
         *
         *   vtime at period start + (wallclock time since the start) * vrate
         *
         * As a consistent snapshot of `period_at_vtime` and `period_at` is
         * needed, they're seqcount protected.
         */
        do {
                seq = read_seqcount_begin(&ioc->period_seqcount);
                now->vnow = ioc->period_at_vtime +
                        (now->now - ioc->period_at) * now->vrate;
        } while (read_seqcount_retry(&ioc->period_seqcount, seq));
}

static void ioc_start_period(struct ioc *ioc, struct ioc_now *now)
{
        WARN_ON_ONCE(ioc->running != IOC_RUNNING);

        write_seqcount_begin(&ioc->period_seqcount);
        ioc->period_at = now->now;
        ioc->period_at_vtime = now->vnow;
        write_seqcount_end(&ioc->period_seqcount);

        ioc->timer.expires = jiffies + usecs_to_jiffies(ioc->period_us);
        add_timer(&ioc->timer);
}

/*
 * Update @iocg's `active` and `inuse` to @active and @inuse, update level
 * weight sums and propagate upwards accordingly. If @save, the current margin
 * is saved to be used as reference for later inuse in-period adjustments.
 */
static void __propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse,
                                bool save, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        int lvl;

        lockdep_assert_held(&ioc->lock);

        /*
         * For an active leaf node, its inuse shouldn't be zero or exceed
         * @active. An active internal node's inuse is solely determined by the
         * inuse to active ratio of its children regardless of @inuse.
         */
        if (list_empty(&iocg->active_list) && iocg->child_active_sum) {
                inuse = DIV64_U64_ROUND_UP(active * iocg->child_inuse_sum,
                                           iocg->child_active_sum);
        } else {
                inuse = clamp_t(u32, inuse, 1, active);
        }

        iocg->last_inuse = iocg->inuse;
        if (save)
                iocg->saved_margin = now->vnow - atomic64_read(&iocg->vtime);

        if (active == iocg->active && inuse == iocg->inuse)
                return;

        for (lvl = iocg->level - 1; lvl >= 0; lvl--) {
                struct ioc_gq *parent = iocg->ancestors[lvl];
                struct ioc_gq *child = iocg->ancestors[lvl + 1];
                u32 parent_active = 0, parent_inuse = 0;

                /* update the level sums */
                parent->child_active_sum += (s32)(active - child->active);
                parent->child_inuse_sum += (s32)(inuse - child->inuse);
                /* apply the updates */
                child->active = active;
                child->inuse = inuse;

                /*
                 * The delta between inuse and active sums indicates that
                 * much of weight is being given away.  Parent's inuse
                 * and active should reflect the ratio.
                 */
                if (parent->child_active_sum) {
                        parent_active = parent->weight;
                        parent_inuse = DIV64_U64_ROUND_UP(
                                parent_active * parent->child_inuse_sum,
                                parent->child_active_sum);
                }

                /* do we need to keep walking up? */
                if (parent_active == parent->active &&
                    parent_inuse == parent->inuse)
                        break;

                active = parent_active;
                inuse = parent_inuse;
        }

        ioc->weights_updated = true;
}

static void commit_weights(struct ioc *ioc)
{
        lockdep_assert_held(&ioc->lock);

        if (ioc->weights_updated) {
                /* paired with rmb in current_hweight(), see there */
                smp_wmb();
                atomic_inc(&ioc->hweight_gen);
                ioc->weights_updated = false;
        }
}

static void propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse,
                              bool save, struct ioc_now *now)
{
        __propagate_weights(iocg, active, inuse, save, now);
        commit_weights(iocg->ioc);
}

static void current_hweight(struct ioc_gq *iocg, u32 *hw_activep, u32 *hw_inusep)
{
        struct ioc *ioc = iocg->ioc;
        int lvl;
        u32 hwa, hwi;
        int ioc_gen;

        /* hot path - if uptodate, use cached */
        ioc_gen = atomic_read(&ioc->hweight_gen);
        if (ioc_gen == iocg->hweight_gen)
                goto out;

        /*
         * Paired with wmb in commit_weights(). If we saw the updated
         * hweight_gen, all the weight updates from __propagate_weights() are
         * visible too.
         *
         * We can race with weight updates during calculation and get it
         * wrong.  However, hweight_gen would have changed and a future
         * reader will recalculate and we're guaranteed to discard the
         * wrong result soon.
         */
        smp_rmb();

        hwa = hwi = WEIGHT_ONE;
        for (lvl = 0; lvl <= iocg->level - 1; lvl++) {
                struct ioc_gq *parent = iocg->ancestors[lvl];
                struct ioc_gq *child = iocg->ancestors[lvl + 1];
                u64 active_sum = READ_ONCE(parent->child_active_sum);
                u64 inuse_sum = READ_ONCE(parent->child_inuse_sum);
                u32 active = READ_ONCE(child->active);
                u32 inuse = READ_ONCE(child->inuse);

                /* we can race with deactivations and either may read as zero */
                if (!active_sum || !inuse_sum)
                        continue;

                active_sum = max_t(u64, active, active_sum);
                hwa = div64_u64((u64)hwa * active, active_sum);

                inuse_sum = max_t(u64, inuse, inuse_sum);
                hwi = div64_u64((u64)hwi * inuse, inuse_sum);
        }

        iocg->hweight_active = max_t(u32, hwa, 1);
        iocg->hweight_inuse = max_t(u32, hwi, 1);
        iocg->hweight_gen = ioc_gen;
out:
        if (hw_activep)
                *hw_activep = iocg->hweight_active;
        if (hw_inusep)
                *hw_inusep = iocg->hweight_inuse;
}

/*
 * Calculate the hweight_inuse @iocg would get with max @inuse assuming all the
 * other weights stay unchanged.
 */
static u32 current_hweight_max(struct ioc_gq *iocg)
{
        u32 hwm = WEIGHT_ONE;
        u32 inuse = iocg->active;
        u64 child_inuse_sum;
        int lvl;

        lockdep_assert_held(&iocg->ioc->lock);

        for (lvl = iocg->level - 1; lvl >= 0; lvl--) {
                struct ioc_gq *parent = iocg->ancestors[lvl];
                struct ioc_gq *child = iocg->ancestors[lvl + 1];

                child_inuse_sum = parent->child_inuse_sum + inuse - child->inuse;
                hwm = div64_u64((u64)hwm * inuse, child_inuse_sum);
                inuse = DIV64_U64_ROUND_UP(parent->active * child_inuse_sum,
                                           parent->child_active_sum);
        }

        return max_t(u32, hwm, 1);
}

static void weight_updated(struct ioc_gq *iocg, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        struct blkcg_gq *blkg = iocg_to_blkg(iocg);
        struct ioc_cgrp *iocc = blkcg_to_iocc(blkg->blkcg);
        u32 weight;

        lockdep_assert_held(&ioc->lock);

        weight = iocg->cfg_weight ?: iocc->dfl_weight;
        if (weight != iocg->weight && iocg->active)
                propagate_weights(iocg, weight, iocg->inuse, true, now);
        iocg->weight = weight;
}

static bool iocg_activate(struct ioc_gq *iocg, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        u64 last_period, cur_period;
        u64 vtime, vtarget;
        int i;

        /*
         * If seem to be already active, just update the stamp to tell the
         * timer that we're still active.  We don't mind occassional races.
         */
        if (!list_empty(&iocg->active_list)) {
                ioc_now(ioc, now);
                cur_period = atomic64_read(&ioc->cur_period);
                if (atomic64_read(&iocg->active_period) != cur_period)
                        atomic64_set(&iocg->active_period, cur_period);
                return true;
        }

        /* racy check on internal node IOs, treat as root level IOs */
        if (iocg->child_active_sum)
                return false;

        spin_lock_irq(&ioc->lock);

        ioc_now(ioc, now);

        /* update period */
        cur_period = atomic64_read(&ioc->cur_period);
        last_period = atomic64_read(&iocg->active_period);
        atomic64_set(&iocg->active_period, cur_period);

        /* already activated or breaking leaf-only constraint? */
        if (!list_empty(&iocg->active_list))
                goto succeed_unlock;
        for (i = iocg->level - 1; i > 0; i--)
                if (!list_empty(&iocg->ancestors[i]->active_list))
                        goto fail_unlock;

        if (iocg->child_active_sum)
                goto fail_unlock;

        /*
         * Always start with the target budget. On deactivation, we throw away
         * anything above it.
         */
        vtarget = now->vnow - ioc->margins.target;
        vtime = atomic64_read(&iocg->vtime);

        atomic64_add(vtarget - vtime, &iocg->vtime);
        atomic64_add(vtarget - vtime, &iocg->done_vtime);
        vtime = vtarget;

        /*
         * Activate, propagate weight and start period timer if not
         * running.  Reset hweight_gen to avoid accidental match from
         * wrapping.
         */
        iocg->hweight_gen = atomic_read(&ioc->hweight_gen) - 1;
        list_add(&iocg->active_list, &ioc->active_iocgs);

        propagate_weights(iocg, iocg->weight,
                          iocg->last_inuse ?: iocg->weight, true, now);

        TRACE_IOCG_PATH(iocg_activate, iocg, now,
                        last_period, cur_period, vtime);

        iocg->activated_at = now->now;

        if (ioc->running == IOC_IDLE) {
                ioc->running = IOC_RUNNING;
                ioc->dfgv_period_at = now->now;
                ioc->dfgv_period_rem = 0;
                ioc_start_period(ioc, now);
        }

succeed_unlock:
        spin_unlock_irq(&ioc->lock);
        return true;

fail_unlock:
        spin_unlock_irq(&ioc->lock);
        return false;
}

static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        struct blkcg_gq *blkg = iocg_to_blkg(iocg);
        u64 tdelta, delay, new_delay;
        s64 vover, vover_pct;
        u32 hwa;

        lockdep_assert_held(&iocg->waitq.lock);

        /* calculate the current delay in effect - 1/2 every second */
        tdelta = now->now - iocg->delay_at;
        if (iocg->delay)
                delay = iocg->delay >> div64_u64(tdelta, USEC_PER_SEC);
        else
                delay = 0;

        /* calculate the new delay from the debt amount */
        current_hweight(iocg, &hwa, NULL);
        vover = atomic64_read(&iocg->vtime) +
                abs_cost_to_cost(iocg->abs_vdebt, hwa) - now->vnow;
        vover_pct = div64_s64(100 * vover,
                              ioc->period_us * ioc->vtime_base_rate);

        if (vover_pct <= MIN_DELAY_THR_PCT)
                new_delay = 0;
        else if (vover_pct >= MAX_DELAY_THR_PCT)
                new_delay = MAX_DELAY;
        else
                new_delay = MIN_DELAY +
                        div_u64((MAX_DELAY - MIN_DELAY) *
                                (vover_pct - MIN_DELAY_THR_PCT),
                                MAX_DELAY_THR_PCT - MIN_DELAY_THR_PCT);

        /* pick the higher one and apply */
        if (new_delay > delay) {
                iocg->delay = new_delay;
                iocg->delay_at = now->now;
                delay = new_delay;
        }

        if (delay >= MIN_DELAY) {
                if (!iocg->indelay_since)
                        iocg->indelay_since = now->now;
                blkcg_set_delay(blkg, delay * NSEC_PER_USEC);
                return true;
        } else {
                if (iocg->indelay_since) {
                        iocg->local_stat.indelay_us += now->now - iocg->indelay_since;
                        iocg->indelay_since = 0;
                }
                iocg->delay = 0;
                blkcg_clear_delay(blkg);
                return false;
        }
}

static void iocg_incur_debt(struct ioc_gq *iocg, u64 abs_cost,
                            struct ioc_now *now)
{
        struct iocg_pcpu_stat *gcs;

        lockdep_assert_held(&iocg->ioc->lock);
        lockdep_assert_held(&iocg->waitq.lock);
        WARN_ON_ONCE(list_empty(&iocg->active_list));

        /*
         * Once in debt, debt handling owns inuse. @iocg stays at the minimum
         * inuse donating all of it share to others until its debt is paid off.
         */
        if (!iocg->abs_vdebt && abs_cost) {
                iocg->indebt_since = now->now;
                propagate_weights(iocg, iocg->active, 0, false, now);
        }

        iocg->abs_vdebt += abs_cost;

        gcs = get_cpu_ptr(iocg->pcpu_stat);
        local64_add(abs_cost, &gcs->abs_vusage);
        put_cpu_ptr(gcs);
}

static void iocg_pay_debt(struct ioc_gq *iocg, u64 abs_vpay,
                          struct ioc_now *now)
{
        lockdep_assert_held(&iocg->ioc->lock);
        lockdep_assert_held(&iocg->waitq.lock);

        /* make sure that nobody messed with @iocg */
        WARN_ON_ONCE(list_empty(&iocg->active_list));
        WARN_ON_ONCE(iocg->inuse > 1);

        iocg->abs_vdebt -= min(abs_vpay, iocg->abs_vdebt);

        /* if debt is paid in full, restore inuse */
        if (!iocg->abs_vdebt) {
                iocg->local_stat.indebt_us += now->now - iocg->indebt_since;
                iocg->indebt_since = 0;

                propagate_weights(iocg, iocg->active, iocg->last_inuse,
                                  false, now);
        }
}

static int iocg_wake_fn(struct wait_queue_entry *wq_entry, unsigned mode,
                        int flags, void *key)
{
        struct iocg_wait *wait = container_of(wq_entry, struct iocg_wait, wait);
        struct iocg_wake_ctx *ctx = (struct iocg_wake_ctx *)key;
        u64 cost = abs_cost_to_cost(wait->abs_cost, ctx->hw_inuse);

        ctx->vbudget -= cost;

        if (ctx->vbudget < 0)
                return -1;

        iocg_commit_bio(ctx->iocg, wait->bio, wait->abs_cost, cost);
        wait->committed = true;

        /*
         * autoremove_wake_function() removes the wait entry only when it
         * actually changed the task state. We want the wait always removed.
         * Remove explicitly and use default_wake_function(). Note that the
         * order of operations is important as finish_wait() tests whether
         * @wq_entry is removed without grabbing the lock.
         */
        default_wake_function(wq_entry, mode, flags, key);
        list_del_init_careful(&wq_entry->entry);
        return 0;
}

/*
 * Calculate the accumulated budget, pay debt if @pay_debt and wake up waiters
 * accordingly. When @pay_debt is %true, the caller must be holding ioc->lock in
 * addition to iocg->waitq.lock.
 */
static void iocg_kick_waitq(struct ioc_gq *iocg, bool pay_debt,
                            struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        struct iocg_wake_ctx ctx = { .iocg = iocg };
        u64 vshortage, expires, oexpires;
        s64 vbudget;
        u32 hwa;

        lockdep_assert_held(&iocg->waitq.lock);

        current_hweight(iocg, &hwa, NULL);
        vbudget = now->vnow - atomic64_read(&iocg->vtime);

        /* pay off debt */
        if (pay_debt && iocg->abs_vdebt && vbudget > 0) {
                u64 abs_vbudget = cost_to_abs_cost(vbudget, hwa);
                u64 abs_vpay = min_t(u64, abs_vbudget, iocg->abs_vdebt);
                u64 vpay = abs_cost_to_cost(abs_vpay, hwa);

                lockdep_assert_held(&ioc->lock);

                atomic64_add(vpay, &iocg->vtime);
                atomic64_add(vpay, &iocg->done_vtime);
                iocg_pay_debt(iocg, abs_vpay, now);
                vbudget -= vpay;
        }

        if (iocg->abs_vdebt || iocg->delay)
                iocg_kick_delay(iocg, now);

        /*
         * Debt can still be outstanding if we haven't paid all yet or the
         * caller raced and called without @pay_debt. Shouldn't wake up waiters
         * under debt. Make sure @vbudget reflects the outstanding amount and is
         * not positive.
         */
        if (iocg->abs_vdebt) {
                s64 vdebt = abs_cost_to_cost(iocg->abs_vdebt, hwa);
                vbudget = min_t(s64, 0, vbudget - vdebt);
        }

        /*
         * Wake up the ones which are due and see how much vtime we'll need for
         * the next one. As paying off debt restores hw_inuse, it must be read
         * after the above debt payment.
         */
        ctx.vbudget = vbudget;
        current_hweight(iocg, NULL, &ctx.hw_inuse);

        __wake_up_locked_key(&iocg->waitq, TASK_NORMAL, &ctx);

        if (!waitqueue_active(&iocg->waitq)) {
                if (iocg->wait_since) {
                        iocg->local_stat.wait_us += now->now - iocg->wait_since;
                        iocg->wait_since = 0;
                }
                return;
        }

        if (!iocg->wait_since)
                iocg->wait_since = now->now;

        if (WARN_ON_ONCE(ctx.vbudget >= 0))
                return;

        /* determine next wakeup, add a timer margin to guarantee chunking */
        vshortage = -ctx.vbudget;
        expires = now->now_ns +
                DIV64_U64_ROUND_UP(vshortage, ioc->vtime_base_rate) *
                NSEC_PER_USEC;
        expires += ioc->timer_slack_ns;

        /* if already active and close enough, don't bother */
        oexpires = ktime_to_ns(hrtimer_get_softexpires(&iocg->waitq_timer));
        if (hrtimer_is_queued(&iocg->waitq_timer) &&
            abs(oexpires - expires) <= ioc->timer_slack_ns)
                return;

        hrtimer_start_range_ns(&iocg->waitq_timer, ns_to_ktime(expires),
                               ioc->timer_slack_ns, HRTIMER_MODE_ABS);
}

static enum hrtimer_restart iocg_waitq_timer_fn(struct hrtimer *timer)
{
        struct ioc_gq *iocg = container_of(timer, struct ioc_gq, waitq_timer);
        bool pay_debt = READ_ONCE(iocg->abs_vdebt);
        struct ioc_now now;
        unsigned long flags;

        ioc_now(iocg->ioc, &now);

        iocg_lock(iocg, pay_debt, &flags);
        iocg_kick_waitq(iocg, pay_debt, &now);
        iocg_unlock(iocg, pay_debt, &flags);

        return HRTIMER_NORESTART;
}

static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p)
{
        u32 nr_met[2] = { };
        u32 nr_missed[2] = { };
        u64 rq_wait_ns = 0;
        int cpu, rw;

        for_each_online_cpu(cpu) {
                struct ioc_pcpu_stat *stat = per_cpu_ptr(ioc->pcpu_stat, cpu);
                u64 this_rq_wait_ns;

                for (rw = READ; rw <= WRITE; rw++) {
                        u32 this_met = local_read(&stat->missed[rw].nr_met);
                        u32 this_missed = local_read(&stat->missed[rw].nr_missed);

                        nr_met[rw] += this_met - stat->missed[rw].last_met;
                        nr_missed[rw] += this_missed - stat->missed[rw].last_missed;
                        stat->missed[rw].last_met = this_met;
                        stat->missed[rw].last_missed = this_missed;
                }

                this_rq_wait_ns = local64_read(&stat->rq_wait_ns);
                rq_wait_ns += this_rq_wait_ns - stat->last_rq_wait_ns;
                stat->last_rq_wait_ns = this_rq_wait_ns;
        }

        for (rw = READ; rw <= WRITE; rw++) {
                if (nr_met[rw] + nr_missed[rw])
                        missed_ppm_ar[rw] =
                                DIV64_U64_ROUND_UP((u64)nr_missed[rw] * MILLION,
                                                   nr_met[rw] + nr_missed[rw]);
                else
                        missed_ppm_ar[rw] = 0;
        }

        *rq_wait_pct_p = div64_u64(rq_wait_ns * 100,
                                   ioc->period_us * NSEC_PER_USEC);
}

/* was iocg idle this period? */
static bool iocg_is_idle(struct ioc_gq *iocg)
{
        struct ioc *ioc = iocg->ioc;

        /* did something get issued this period? */
        if (atomic64_read(&iocg->active_period) ==
            atomic64_read(&ioc->cur_period))
                return false;

        /* is something in flight? */
        if (atomic64_read(&iocg->done_vtime) != atomic64_read(&iocg->vtime))
                return false;

        return true;
}

/*
 * Call this function on the target leaf @iocg's to build pre-order traversal
 * list of all the ancestors in @inner_walk. The inner nodes are linked through
 * ->walk_list and the caller is responsible for dissolving the list after use.
 */
static void iocg_build_inner_walk(struct ioc_gq *iocg,
                                  struct list_head *inner_walk)
{
        int lvl;

        WARN_ON_ONCE(!list_empty(&iocg->walk_list));

        /* find the first ancestor which hasn't been visited yet */
        for (lvl = iocg->level - 1; lvl >= 0; lvl--) {
                if (!list_empty(&iocg->ancestors[lvl]->walk_list))
                        break;
        }

        /* walk down and visit the inner nodes to get pre-order traversal */
        while (++lvl <= iocg->level - 1) {
                struct ioc_gq *inner = iocg->ancestors[lvl];

                /* record traversal order */
                list_add_tail(&inner->walk_list, inner_walk);
        }
}

/* collect per-cpu counters and propagate the deltas to the parent */
static void iocg_flush_stat_one(struct ioc_gq *iocg, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        struct iocg_stat new_stat;
        u64 abs_vusage = 0;
        u64 vusage_delta;
        int cpu;

        lockdep_assert_held(&iocg->ioc->lock);

        /* collect per-cpu counters */
        for_each_possible_cpu(cpu) {
                abs_vusage += local64_read(
                                per_cpu_ptr(&iocg->pcpu_stat->abs_vusage, cpu));
        }
        vusage_delta = abs_vusage - iocg->last_stat_abs_vusage;
        iocg->last_stat_abs_vusage = abs_vusage;

        iocg->usage_delta_us = div64_u64(vusage_delta, ioc->vtime_base_rate);
        iocg->local_stat.usage_us += iocg->usage_delta_us;

        /* propagate upwards */
        new_stat.usage_us =
                iocg->local_stat.usage_us + iocg->desc_stat.usage_us;
        new_stat.wait_us =
                iocg->local_stat.wait_us + iocg->desc_stat.wait_us;
        new_stat.indebt_us =
                iocg->local_stat.indebt_us + iocg->desc_stat.indebt_us;
        new_stat.indelay_us =
                iocg->local_stat.indelay_us + iocg->desc_stat.indelay_us;

        /* propagate the deltas to the parent */
        if (iocg->level > 0) {
                struct iocg_stat *parent_stat =
                        &iocg->ancestors[iocg->level - 1]->desc_stat;

                parent_stat->usage_us +=
                        new_stat.usage_us - iocg->last_stat.usage_us;
                parent_stat->wait_us +=
                        new_stat.wait_us - iocg->last_stat.wait_us;
                parent_stat->indebt_us +=
                        new_stat.indebt_us - iocg->last_stat.indebt_us;
                parent_stat->indelay_us +=
                        new_stat.indelay_us - iocg->last_stat.indelay_us;
        }

        iocg->last_stat = new_stat;
}

/* get stat counters ready for reading on all active iocgs */
static void iocg_flush_stat(struct list_head *target_iocgs, struct ioc_now *now)
{
        LIST_HEAD(inner_walk);
        struct ioc_gq *iocg, *tiocg;

        /* flush leaves and build inner node walk list */
        list_for_each_entry(iocg, target_iocgs, active_list) {
                iocg_flush_stat_one(iocg, now);
                iocg_build_inner_walk(iocg, &inner_walk);
        }

        /* keep flushing upwards by walking the inner list backwards */
        list_for_each_entry_safe_reverse(iocg, tiocg, &inner_walk, walk_list) {
                iocg_flush_stat_one(iocg, now);
                list_del_init(&iocg->walk_list);
        }
}

/*
 * Determine what @iocg's hweight_inuse should be after donating unused
 * capacity. @hwm is the upper bound and used to signal no donation. This
 * function also throws away @iocg's excess budget.
 */
static u32 hweight_after_donation(struct ioc_gq *iocg, u32 old_hwi, u32 hwm,
                                  u32 usage, struct ioc_now *now)
{
        struct ioc *ioc = iocg->ioc;
        u64 vtime = atomic64_read(&iocg->vtime);
        s64 excess, delta, target, new_hwi;

        /* debt handling owns inuse for debtors */
        if (iocg->abs_vdebt)
                return 1;

        /* see whether minimum margin requirement is met */
        if (waitqueue_active(&iocg->waitq) ||
            time_after64(vtime, now->vnow - ioc->margins.min))
                return hwm;

        /* throw away excess above target */
        excess = now->vnow - vtime - ioc->margins.target;
        if (excess > 0) {
                atomic64_add(excess, &iocg->vtime);
                atomic64_add(excess, &iocg->done_vtime);
                vtime += excess;
                ioc->vtime_err -= div64_u64(excess * old_hwi, WEIGHT_ONE);
        }

        /*
         * Let's say the distance between iocg's and device's vtimes as a
         * fraction of period duration is delta. Assuming that the iocg will
         * consume the usage determined above, we want to determine new_hwi so
         * that delta equals MARGIN_TARGET at the end of the next period.
         *
         * We need to execute usage worth of IOs while spending the sum of the
         * new budget (1 - MARGIN_TARGET) and the leftover from the last period
         * (delta):
         *
         *   usage = (1 - MARGIN_TARGET + delta) * new_hwi
         *
         * Therefore, the new_hwi is:
         *
         *   new_hwi = usage / (1 - MARGIN_TARGET + delta)
         */
        delta = div64_s64(WEIGHT_ONE * (now->vnow - vtime),
                          now->vnow - ioc->period_at_vtime);
        target = WEIGHT_ONE * MARGIN_TARGET_PCT / 100;
        new_hwi = div64_s64(WEIGHT_ONE * usage, WEIGHT_ONE - target + delta);

        return clamp_t(s64, new_hwi, 1, hwm);
}

/*
 * For work-conservation, an iocg which isn't using all of its share should
 * donate the leftover to other iocgs. There are two ways to achieve this - 1.
 * bumping up vrate accordingly 2. lowering the donating iocg's inuse weight.
 *
 * #1 is mathematically simpler but has the drawback of requiring synchronous
 * global hweight_inuse updates when idle iocg's get activated or inuse weights
 * change due to donation snapbacks as it has the possibility of grossly
 * overshooting what's allowed by the model and vrate.
 *
 * #2 is inherently safe with local operations. The donating iocg can easily
 * snap back to higher weights when needed without worrying about impacts on
 * other nodes as the impacts will be inherently correct. This also makes idle
 * iocg activations safe. The only effect activations have is decreasing
 * hweight_inuse of others, the right solution to which is for those iocgs to
 * snap back to higher weights.
 *
 * So, we go with #2. The challenge is calculating how each donating iocg's
 * inuse should be adjusted to achieve the target donation amounts. This is done
 * using Andy's method described in the following pdf.
 *
 *   https://drive.google.com/file/d/1PsJwxPFtjUnwOY1QJ5AeICCcsL7BM3bo
 *
 * Given the weights and target after-donation hweight_inuse values, Andy's
 * method determines how the proportional distribution should look like at each
 * sibling level to maintain the relative relationship between all non-donating
 * pairs. To roughly summarize, it divides the tree into donating and
 * non-donating parts, calculates global donation rate which is used to
 * determine the target hweight_inuse for each node, and then derives per-level
 * proportions.
 *
 * The following pdf shows that global distribution calculated this way can be
 * achieved by scaling inuse weights of donating leaves and propagating the
 * adjustments upwards proportionally.
 *
 *   https://drive.google.com/file/d/1vONz1-fzVO7oY5DXXsLjSxEtYYQbOvsE
 *
 * Combining the above two, we can determine how each leaf iocg's inuse should
 * be adjusted to achieve the target donation.
 *
 *   https://drive.google.com/file/d/1WcrltBOSPN0qXVdBgnKm4mdp9FhuEFQN
 *
 * The inline comments use symbols from the last pdf.
 *
 *   b is the sum of the absolute budgets in the subtree. 1 for the root node.
 *   f is the sum of the absolute budgets of non-donating nodes in the subtree.
 *   t is the sum of the absolute budgets of donating nodes in the subtree.
 *   w is the weight of the node. w = w_f + w_t
 *   w_f is the non-donating portion of w. w_f = w * f / b
 *   w_b is the donating portion of w. w_t = w * t / b
 *   s is the sum of all sibling weights. s = Sum(w) for siblings
 *   s_f and s_t are the non-donating and donating portions of s.
 *
 * Subscript p denotes the parent's counterpart and ' the adjusted value - e.g.
 * w_pt is the donating portion of the parent's weight and w'_pt the same value
 * after adjustments. Subscript r denotes the root node's values.
 */
static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now)
{
        LIST_HEAD(over_hwa);
        LIST_HEAD(inner_walk);
        struct ioc_gq *iocg, *tiocg, *root_iocg;
        u32 after_sum, over_sum, over_target, gamma;

        /*
         * It's pretty unlikely but possible for the total sum of
         * hweight_after_donation's to be higher than WEIGHT_ONE, which will
         * confuse the following calculations. If such condition is detected,
         * scale down everyone over its full share equally to keep the sum below
         * WEIGHT_ONE.
         */
        after_sum = 0;
        over_sum = 0;
        list_for_each_entry(iocg, surpluses, surplus_list) {
                u32 hwa;

                current_hweight(iocg, &hwa, NULL);
                after_sum += iocg->hweight_after_donation;

                if (iocg->hweight_after_donation > hwa) {
                        over_sum += iocg->hweight_after_donation;
                        list_add(&iocg->walk_list, &over_hwa);
                }
        }

        if (after_sum >= WEIGHT_ONE) {
                /*
                 * The delta should be deducted from the over_sum, calculate
                 * target over_sum value.
                 */
                u32 over_delta = after_sum - (WEIGHT_ONE - 1);
                WARN_ON_ONCE(over_sum <= over_delta);
                over_target = over_sum - over_delta;
        } else {
                over_target = 0;
        }

        list_for_each_entry_safe(iocg, tiocg, &over_hwa, walk_list) {
                if (over_target)
                        iocg->hweight_after_donation =
                                div_u64((u64)iocg->hweight_after_donation *
                                        over_target, over_sum);
                list_del_init(&iocg->walk_list);
        }

        /*
         * Build pre-order inner node walk list and prepare for donation
         * adjustment calculations.
         */
        list_for_each_entry(iocg, surpluses, surplus_list) {
                iocg_build_inner_walk(iocg, &inner_walk);
        }

        root_iocg = list_first_entry(&inner_walk, struct ioc_gq, walk_list);
        WARN_ON_ONCE(root_iocg->level > 0);

        list_for_each_entry(iocg, &inner_walk, walk_list) {
                iocg->child_adjusted_sum = 0;
                iocg->hweight_donating = 0;
                iocg->hweight_after_donation = 0;
        }

        /*
         * Propagate the donating budget (b_t) and after donation budget (b'_t)
         * up the hierarchy.
         */
        list_for_each_entry(iocg, surpluses, surplus_list) {
                struct ioc_gq *parent = iocg->ancestors[iocg->level - 1];

                parent->hweight_donating += iocg->hweight_donating;
                parent->hweight_after_donation += iocg->hweight_after_donation;
        }

        list_for_each_entry_reverse(iocg, &inner_walk, walk_list) {
                if (iocg->level > 0) {
                        struct ioc_gq *parent = iocg->ancestors[iocg->level - 1];

                        parent->hweight_donating += iocg->hweight_donating;
                        parent->hweight_after_donation += iocg->hweight_after_donation;
                }
        }

        /*
         * Calculate inner hwa's (b) and make sure the donation values are
         * within the accepted ranges as we're doing low res calculations with
         * roundups.
         */
        list_for_each_entry(iocg, &inner_walk, walk_list) {
                if (iocg->level) {
                        struct ioc_gq *parent = iocg->ancestors[iocg->level - 1];

                        iocg->hweight_active = DIV64_U64_ROUND_UP(
                                (u64)parent->hweight_active * iocg->active,
                                parent->child_active_sum);

                }

                iocg->hweight_donating = min(iocg->hweight_donating,
                                             iocg->hweight_active);
                iocg->hweight_after_donation = min(iocg->hweight_after_donation,
                                                   iocg->hweight_donating - 1);
                if (WARN_ON_ONCE(iocg->hweight_active <= 1 ||
                                 iocg->hweight_donating <= 1 ||
                                 iocg->hweight_after_donation == 0)) {
                        pr_warn("iocg: invalid donation weights in ");
                        pr_cont_cgroup_path(iocg_to_blkg(iocg)->blkcg->css.cgroup);
                        pr_cont(": active=%u donating=%u after=%u\n",
                                iocg->hweight_active, iocg->hweight_donating,
                                iocg->hweight_after_donation);
                }
        }

        /*
         * Calculate the global donation rate (gamma) - the rate to adjust
         * non-donating budgets by.
         *
         * No need to use 64bit multiplication here as the first operand is
         * guaranteed to be smaller than WEIGHT_ONE (1<<16).
         *
         * We know that there are beneficiary nodes and the sum of the donating
         * hweights can't be whole; however, due to the round-ups during hweight
         * calculations, root_iocg->hweight_donating might still end up equal to
         * or greater than whole. Limit the range when calculating the divider.
         *
         * gamma = (1 - t_r') / (1 - t_r)
         */
        gamma = DIV_ROUND_UP(
                (WEIGHT_ONE - root_iocg->hweight_after_donation) * WEIGHT_ONE,
                WEIGHT_ONE - min_t(u32, root_iocg->hweight_donating, WEIGHT_ONE - 1));

        /*
         * Calculate adjusted hwi, child_adjusted_sum and inuse for the inner
         * nodes.
         */
        list_for_each_entry(iocg, &inner_walk, walk_list) {
                struct ioc_gq *parent;
                u32 inuse, wpt, wptp;
                u64 st, sf;

                if (iocg->level == 0) {
                        /* adjusted weight sum for 1st level: s' = s * b_pf / b'_pf */
                        iocg->child_adjusted_sum = DIV64_U64_ROUND_UP(
                                iocg->child_active_sum * (WEIGHT_ONE - iocg->hweight_donating),
                                WEIGHT_ONE - iocg->hweight_after_donation);
                        continue;
                }

                parent = iocg->ancestors[iocg->level - 1];

                /* b' = gamma * b_f + b_t' */
                iocg->hweight_inuse = DIV64_U64_ROUND_UP(
                        (u64)gamma * (iocg->hweight_active - iocg->hweight_donating),
                        WEIGHT_ONE) + iocg->hweight_after_donation;

                /* w' = s' * b' / b'_p */
                inuse = DIV64_U64_ROUND_UP(
                        (u64)parent->child_adjusted_sum * iocg->hweight_inuse,
                        parent->hweight_inuse);

                /* adjusted weight sum for children: s' = s_f + s_t * w'_pt / w_pt */
                st = DIV64_U64_ROUND_UP(
                        iocg->child_active_sum * iocg->hweight_donating,
                        iocg->hweight_active);
                sf = iocg->child_active_sum - st;
                wpt = DIV64_U64_ROUND_UP(
                        (u64)iocg->active * iocg->hweight_donating,
                        iocg->hweight_active);
                wptp = DIV64_U64_ROUND_UP(
                        (u64)inuse * iocg->hweight_after_donation,
                        iocg->hweight_inuse);

                iocg->child_adjusted_sum = sf + DIV64_U64_ROUND_UP(st * wptp, wpt);
        }