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 #define MIN(x, y) ((x) < (y) ? (x) : (y)) 38 39 static void busy_wait(ulong time) 40 { 41 u64 start, end; 42 43 start = trace_clock_local(); 44 45 do { 46 end = trace_clock_local(); 47 if (kthread_should_stop()) 48 break; 49 } while ((end - start) < (time * 1000)); 50 } 51 52 static __always_inline void irqoff_test(void) 53 { 54 unsigned long flags; 55 56 local_irq_save(flags); 57 busy_wait(delay); 58 local_irq_restore(flags); 59 } 60 61 static __always_inline void preemptoff_test(void) 62 { 63 preempt_disable(); 64 busy_wait(delay); 65 preempt_enable(); 66 } 67 68 static void execute_preemptirqtest(int idx) 69 { 70 if (!strcmp(test_mode, "irq")) 71 irqoff_test(); 72 else if (!strcmp(test_mode, "preempt")) 73 preemptoff_test(); 74 else if (!strcmp(test_mode, "alternate")) { 75 if (idx % 2 == 0) 76 irqoff_test(); 77 else 78 preemptoff_test(); 79 } 80 } 81 82 #define DECLARE_TESTFN(POSTFIX) \ 83 static void preemptirqtest_##POSTFIX(int idx) \ 84 { \ 85 execute_preemptirqtest(idx); \ 86 } \ 87 88 /* 89 * We create 10 different functions, so that we can get 10 different 90 * backtraces. 91 */ 92 DECLARE_TESTFN(0) 93 DECLARE_TESTFN(1) 94 DECLARE_TESTFN(2) 95 DECLARE_TESTFN(3) 96 DECLARE_TESTFN(4) 97 DECLARE_TESTFN(5) 98 DECLARE_TESTFN(6) 99 DECLARE_TESTFN(7) 100 DECLARE_TESTFN(8) 101 DECLARE_TESTFN(9) 102 103 static void (*testfuncs[])(int) = { 104 preemptirqtest_0, 105 preemptirqtest_1, 106 preemptirqtest_2, 107 preemptirqtest_3, 108 preemptirqtest_4, 109 preemptirqtest_5, 110 preemptirqtest_6, 111 preemptirqtest_7, 112 preemptirqtest_8, 113 preemptirqtest_9, 114 }; 115 116 #define NR_TEST_FUNCS ARRAY_SIZE(testfuncs) 117 118 static int preemptirq_delay_run(void *data) 119 { 120 int i; 121 int s = MIN(burst_size, NR_TEST_FUNCS); 122 struct cpumask cpu_mask; 123 124 if (cpu_affinity > -1) { 125 cpumask_clear(&cpu_mask); 126 cpumask_set_cpu(cpu_affinity, &cpu_mask); 127 if (set_cpus_allowed_ptr(current, &cpu_mask)) 128 pr_err("cpu_affinity:%d, failed\n", cpu_affinity); 129 } 130 131 for (i = 0; i < s; i++) 132 (testfuncs[i])(i); 133 134 complete(&done); 135 136 set_current_state(TASK_INTERRUPTIBLE); 137 while (!kthread_should_stop()) { 138 schedule(); 139 set_current_state(TASK_INTERRUPTIBLE); 140 } 141 142 __set_current_state(TASK_RUNNING); 143 144 return 0; 145 } 146 147 static int preemptirq_run_test(void) 148 { 149 struct task_struct *task; 150 char task_name[50]; 151 152 init_completion(&done); 153 154 snprintf(task_name, sizeof(task_name), "%s_test", test_mode); 155 task = kthread_run(preemptirq_delay_run, NULL, task_name); 156 if (IS_ERR(task)) 157 return PTR_ERR(task); 158 if (task) { 159 wait_for_completion(&done); 160 kthread_stop(task); 161 } 162 return 0; 163 } 164 165 166 static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr, 167 const char *buf, size_t count) 168 { 169 ssize_t ret; 170 171 ret = preemptirq_run_test(); 172 if (ret) 173 return ret; 174 return count; 175 } 176 177 static struct kobj_attribute trigger_attribute = 178 __ATTR(trigger, 0200, NULL, trigger_store); 179 180 static struct attribute *attrs[] = { 181 &trigger_attribute.attr, 182 NULL, 183 }; 184 185 static struct attribute_group attr_group = { 186 .attrs = attrs, 187 }; 188 189 static struct kobject *preemptirq_delay_kobj; 190 191 static int __init preemptirq_delay_init(void) 192 { 193 int retval; 194 195 retval = preemptirq_run_test(); 196 if (retval != 0) 197 return retval; 198 199 preemptirq_delay_kobj = kobject_create_and_add("preemptirq_delay_test", 200 kernel_kobj); 201 if (!preemptirq_delay_kobj) 202 return -ENOMEM; 203 204 retval = sysfs_create_group(preemptirq_delay_kobj, &attr_group); 205 if (retval) 206 kobject_put(preemptirq_delay_kobj); 207 208 return retval; 209 } 210 211 static void __exit preemptirq_delay_exit(void) 212 { 213 kobject_put(preemptirq_delay_kobj); 214 } 215 216 module_init(preemptirq_delay_init) 217 module_exit(preemptirq_delay_exit) 218 MODULE_LICENSE("GPL v2"); 219