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