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
busy_wait(ulong time)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
irqoff_test(void)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
preemptoff_test(void)61 static __always_inline void preemptoff_test(void)
62 {
63 preempt_disable();
64 busy_wait(delay);
65 preempt_enable();
66 }
67
execute_preemptirqtest(int idx)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
preemptirq_delay_run(void * data)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
preemptirq_run_test(void)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
trigger_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)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
preemptirq_delay_init(void)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
preemptirq_delay_exit(void)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