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