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"); 218