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