linux/kernel/trace/preemptirq_delay_test.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Preempt / IRQ disable delay thread to test latency tracers
   4 *
   5 * Copyright (C) 2018 Joel Fernandes (Google) <joel@joelfernandes.org>
   6 */
   7
   8#include <linux/trace_clock.h>
   9#include <linux/delay.h>
  10#include <linux/interrupt.h>
  11#include <linux/irq.h>
  12#include <linux/kernel.h>
  13#include <linux/kobject.h>
  14#include <linux/kthread.h>
  15#include <linux/module.h>
  16#include <linux/printk.h>
  17#include <linux/string.h>
  18#include <linux/sysfs.h>
  19#include <linux/completion.h>
  20
  21static ulong delay = 100;
  22static char test_mode[12] = "irq";
  23static uint burst_size = 1;
  24static int  cpu_affinity = -1;
  25
  26module_param_named(delay, delay, ulong, 0444);
  27module_param_string(test_mode, test_mode, 12, 0444);
  28module_param_named(burst_size, burst_size, uint, 0444);
  29module_param_named(cpu_affinity, cpu_affinity, int, 0444);
  30MODULE_PARM_DESC(delay, "Period in microseconds (100 us default)");
  31MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or alternate (default irq)");
  32MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
  33MODULE_PARM_DESC(cpu_affinity, "Cpu num test is running on");
  34
  35static struct completion done;
  36
  37#define MIN(x, y) ((x) < (y) ? (x) : (y))
  38
  39static void busy_wait(ulong time)
  40{
  41        u64 start, end;
  42
  43        start = trace_clock_local();
  44
  45        do {
  46                end = trace_clock_local();
  47                if (kthread_should_stop())
  48                        break;
  49        } while ((end - start) < (time * 1000));
  50}
  51
  52static __always_inline void irqoff_test(void)
  53{
  54        unsigned long flags;
  55
  56        local_irq_save(flags);
  57        busy_wait(delay);
  58        local_irq_restore(flags);
  59}
  60
  61static __always_inline void preemptoff_test(void)
  62{
  63        preempt_disable();
  64        busy_wait(delay);
  65        preempt_enable();
  66}
  67
  68static void execute_preemptirqtest(int idx)
  69{
  70        if (!strcmp(test_mode, "irq"))
  71                irqoff_test();
  72        else if (!strcmp(test_mode, "preempt"))
  73                preemptoff_test();
  74        else if (!strcmp(test_mode, "alternate")) {
  75                if (idx % 2 == 0)
  76                        irqoff_test();
  77                else
  78                        preemptoff_test();
  79        }
  80}
  81
  82#define DECLARE_TESTFN(POSTFIX)                         \
  83        static void preemptirqtest_##POSTFIX(int idx)   \
  84        {                                               \
  85                execute_preemptirqtest(idx);            \
  86        }                                               \
  87
  88/*
  89 * We create 10 different functions, so that we can get 10 different
  90 * backtraces.
  91 */
  92DECLARE_TESTFN(0)
  93DECLARE_TESTFN(1)
  94DECLARE_TESTFN(2)
  95DECLARE_TESTFN(3)
  96DECLARE_TESTFN(4)
  97DECLARE_TESTFN(5)
  98DECLARE_TESTFN(6)
  99DECLARE_TESTFN(7)
 100DECLARE_TESTFN(8)
 101DECLARE_TESTFN(9)
 102
 103static void (*testfuncs[])(int)  = {
 104        preemptirqtest_0,
 105        preemptirqtest_1,
 106        preemptirqtest_2,
 107        preemptirqtest_3,
 108        preemptirqtest_4,
 109        preemptirqtest_5,
 110        preemptirqtest_6,
 111        preemptirqtest_7,
 112        preemptirqtest_8,
 113        preemptirqtest_9,
 114};
 115
 116#define NR_TEST_FUNCS ARRAY_SIZE(testfuncs)
 117
 118static int preemptirq_delay_run(void *data)
 119{
 120        int i;
 121        int s = MIN(burst_size, NR_TEST_FUNCS);
 122        struct cpumask cpu_mask;
 123
 124        if (cpu_affinity > -1) {
 125                cpumask_clear(&cpu_mask);
 126                cpumask_set_cpu(cpu_affinity, &cpu_mask);
 127                if (set_cpus_allowed_ptr(current, &cpu_mask))
 128                        pr_err("cpu_affinity:%d, failed\n", cpu_affinity);
 129        }
 130
 131        for (i = 0; i < s; i++)
 132                (testfuncs[i])(i);
 133
 134        complete(&done);
 135
 136        set_current_state(TASK_INTERRUPTIBLE);
 137        while (!kthread_should_stop()) {
 138                schedule();
 139                set_current_state(TASK_INTERRUPTIBLE);
 140        }
 141
 142        __set_current_state(TASK_RUNNING);
 143
 144        return 0;
 145}
 146
 147static int preemptirq_run_test(void)
 148{
 149        struct task_struct *task;
 150        char task_name[50];
 151
 152        init_completion(&done);
 153
 154        snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
 155        task =  kthread_run(preemptirq_delay_run, NULL, task_name);
 156        if (IS_ERR(task))
 157                return PTR_ERR(task);
 158        if (task) {
 159                wait_for_completion(&done);
 160                kthread_stop(task);
 161        }
 162        return 0;
 163}
 164
 165
 166static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr,
 167                         const char *buf, size_t count)
 168{
 169        ssize_t ret;
 170
 171        ret = preemptirq_run_test();
 172        if (ret)
 173                return ret;
 174        return count;
 175}
 176
 177static struct kobj_attribute trigger_attribute =
 178        __ATTR(trigger, 0200, NULL, trigger_store);
 179
 180static struct attribute *attrs[] = {
 181        &trigger_attribute.attr,
 182        NULL,
 183};
 184
 185static struct attribute_group attr_group = {
 186        .attrs = attrs,
 187};
 188
 189static struct kobject *preemptirq_delay_kobj;
 190
 191static int __init preemptirq_delay_init(void)
 192{
 193        int retval;
 194
 195        retval = preemptirq_run_test();
 196        if (retval != 0)
 197                return retval;
 198
 199        preemptirq_delay_kobj = kobject_create_and_add("preemptirq_delay_test",
 200                                                       kernel_kobj);
 201        if (!preemptirq_delay_kobj)
 202                return -ENOMEM;
 203
 204        retval = sysfs_create_group(preemptirq_delay_kobj, &attr_group);
 205        if (retval)
 206                kobject_put(preemptirq_delay_kobj);
 207
 208        return retval;
 209}
 210
 211static void __exit preemptirq_delay_exit(void)
 212{
 213        kobject_put(preemptirq_delay_kobj);
 214}
 215
 216module_init(preemptirq_delay_init)
 217module_exit(preemptirq_delay_exit)
 218MODULE_LICENSE("GPL v2");
 219
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