linux/net/rds/ib_ring.c
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   1/*
   2 * Copyright (c) 2006 Oracle.  All rights reserved.
   3 *
   4 * This software is available to you under a choice of one of two
   5 * licenses.  You may choose to be licensed under the terms of the GNU
   6 * General Public License (GPL) Version 2, available from the file
   7 * COPYING in the main directory of this source tree, or the
   8 * OpenIB.org BSD license below:
   9 *
  10 *     Redistribution and use in source and binary forms, with or
  11 *     without modification, are permitted provided that the following
  12 *     conditions are met:
  13 *
  14 *      - Redistributions of source code must retain the above
  15 *        copyright notice, this list of conditions and the following
  16 *        disclaimer.
  17 *
  18 *      - Redistributions in binary form must reproduce the above
  19 *        copyright notice, this list of conditions and the following
  20 *        disclaimer in the documentation and/or other materials
  21 *        provided with the distribution.
  22 *
  23 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  24 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  25 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  26 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  27 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  28 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  29 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  30 * SOFTWARE.
  31 *
  32 */
  33#include <linux/kernel.h>
  34
  35#include "rds.h"
  36#include "ib.h"
  37
  38/*
  39 * Locking for IB rings.
  40 * We assume that allocation is always protected by a mutex
  41 * in the caller (this is a valid assumption for the current
  42 * implementation).
  43 *
  44 * Freeing always happens in an interrupt, and hence only
  45 * races with allocations, but not with other free()s.
  46 *
  47 * The interaction between allocation and freeing is that
  48 * the alloc code has to determine the number of free entries.
  49 * To this end, we maintain two counters; an allocation counter
  50 * and a free counter. Both are allowed to run freely, and wrap
  51 * around.
  52 * The number of used entries is always (alloc_ctr - free_ctr) % NR.
  53 *
  54 * The current implementation makes free_ctr atomic. When the
  55 * caller finds an allocation fails, it should set an "alloc fail"
  56 * bit and retry the allocation. The "alloc fail" bit essentially tells
  57 * the CQ completion handlers to wake it up after freeing some
  58 * more entries.
  59 */
  60
  61/*
  62 * This only happens on shutdown.
  63 */
  64DECLARE_WAIT_QUEUE_HEAD(rds_ib_ring_empty_wait);
  65
  66void rds_ib_ring_init(struct rds_ib_work_ring *ring, u32 nr)
  67{
  68        memset(ring, 0, sizeof(*ring));
  69        ring->w_nr = nr;
  70        rdsdebug("ring %p nr %u\n", ring, ring->w_nr);
  71}
  72
  73static inline u32 __rds_ib_ring_used(struct rds_ib_work_ring *ring)
  74{
  75        u32 diff;
  76
  77        /* This assumes that atomic_t has at least as many bits as u32 */
  78        diff = ring->w_alloc_ctr - (u32) atomic_read(&ring->w_free_ctr);
  79        BUG_ON(diff > ring->w_nr);
  80
  81        return diff;
  82}
  83
  84void rds_ib_ring_resize(struct rds_ib_work_ring *ring, u32 nr)
  85{
  86        /* We only ever get called from the connection setup code,
  87         * prior to creating the QP. */
  88        BUG_ON(__rds_ib_ring_used(ring));
  89        ring->w_nr = nr;
  90}
  91
  92static int __rds_ib_ring_empty(struct rds_ib_work_ring *ring)
  93{
  94        return __rds_ib_ring_used(ring) == 0;
  95}
  96
  97u32 rds_ib_ring_alloc(struct rds_ib_work_ring *ring, u32 val, u32 *pos)
  98{
  99        u32 ret = 0, avail;
 100
 101        avail = ring->w_nr - __rds_ib_ring_used(ring);
 102
 103        rdsdebug("ring %p val %u next %u free %u\n", ring, val,
 104                 ring->w_alloc_ptr, avail);
 105
 106        if (val && avail) {
 107                ret = min(val, avail);
 108                *pos = ring->w_alloc_ptr;
 109
 110                ring->w_alloc_ptr = (ring->w_alloc_ptr + ret) % ring->w_nr;
 111                ring->w_alloc_ctr += ret;
 112        }
 113
 114        return ret;
 115}
 116
 117void rds_ib_ring_free(struct rds_ib_work_ring *ring, u32 val)
 118{
 119        ring->w_free_ptr = (ring->w_free_ptr + val) % ring->w_nr;
 120        atomic_add(val, &ring->w_free_ctr);
 121
 122        if (__rds_ib_ring_empty(ring) &&
 123            waitqueue_active(&rds_ib_ring_empty_wait))
 124                wake_up(&rds_ib_ring_empty_wait);
 125}
 126
 127void rds_ib_ring_unalloc(struct rds_ib_work_ring *ring, u32 val)
 128{
 129        ring->w_alloc_ptr = (ring->w_alloc_ptr - val) % ring->w_nr;
 130        ring->w_alloc_ctr -= val;
 131}
 132
 133int rds_ib_ring_empty(struct rds_ib_work_ring *ring)
 134{
 135        return __rds_ib_ring_empty(ring);
 136}
 137
 138int rds_ib_ring_low(struct rds_ib_work_ring *ring)
 139{
 140        return __rds_ib_ring_used(ring) <= (ring->w_nr >> 1);
 141}
 142
 143/*
 144 * returns the oldest alloced ring entry.  This will be the next one
 145 * freed.  This can't be called if there are none allocated.
 146 */
 147u32 rds_ib_ring_oldest(struct rds_ib_work_ring *ring)
 148{
 149        return ring->w_free_ptr;
 150}
 151
 152/*
 153 * returns the number of completed work requests.
 154 */
 155
 156u32 rds_ib_ring_completed(struct rds_ib_work_ring *ring, u32 wr_id, u32 oldest)
 157{
 158        u32 ret;
 159
 160        if (oldest <= (unsigned long long)wr_id)
 161                ret = (unsigned long long)wr_id - oldest + 1;
 162        else
 163                ret = ring->w_nr - oldest + (unsigned long long)wr_id + 1;
 164
 165        rdsdebug("ring %p ret %u wr_id %u oldest %u\n", ring, ret,
 166                 wr_id, oldest);
 167        return ret;
 168}
 169
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