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_DESCRIPTION("Preempt / IRQ disable delay thread to test latency tracers");
219 MODULE_LICENSE("GPL v2");
220