kernel/trace/preemptirq_delay_test.c

   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/kthread.h>
  14 #include <linux/module.h>
  15 #include <linux/printk.h>
  16 #include <linux/string.h>
  17
  18 static ulong delay = 100;
  19 static char test_mode[10] = "irq";
  20
  21 module_param_named(delay, delay, ulong, S_IRUGO);
  22 module_param_string(test_mode, test_mode, 10, S_IRUGO);
  23 MODULE_PARM_DESC(delay, "Period in microseconds (100 uS default)");
  24 MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt or irq (default irq)");
  25
  26 static void busy_wait(ulong time)
  27 {
  28         u64 start, end;
  29         start = trace_clock_local();
  30         do {
  31                 end = trace_clock_local();
  32                 if (kthread_should_stop())
  33                         break;
  34         } while ((end - start) < (time * 1000));
  35 }
  36
  37 static int preemptirq_delay_run(void *data)
  38 {
  39         unsigned long flags;
  40
  41         if (!strcmp(test_mode, "irq")) {
  42                 local_irq_save(flags);
  43                 busy_wait(delay);
  44                 local_irq_restore(flags);
  45         } else if (!strcmp(test_mode, "preempt")) {
  46                 preempt_disable();
  47                 busy_wait(delay);
  48                 preempt_enable();
  49         }
  50
  51         return 0;
  52 }
  53
  54 static int __init preemptirq_delay_init(void)
  55 {
  56         char task_name[50];
  57         struct task_struct *test_task;
  58
  59         snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
  60
  61         test_task = kthread_run(preemptirq_delay_run, NULL, task_name);
  62         return PTR_ERR_OR_ZERO(test_task);
  63 }
  64
  65 static void __exit preemptirq_delay_exit(void)
  66 {
  67         return;
  68 }
  69
  70 module_init(preemptirq_delay_init)
  71 module_exit(preemptirq_delay_exit)
  72 MODULE_LICENSE("GPL v2");