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 
20 static ulong delay = 100;
21 static char test_mode[12] = "irq";
22 static uint burst_size = 1;
23 
24 module_param_named(delay, delay, ulong, 0444);
25 module_param_string(test_mode, test_mode, 12, 0444);
26 module_param_named(burst_size, burst_size, uint, 0444);
27 MODULE_PARM_DESC(delay, "Period in microseconds (100 us default)");
28 MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or alternate (default irq)");
29 MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
30 
31 #define MIN(x, y) ((x) < (y) ? (x) : (y))
32 
33 static void busy_wait(ulong time)
34 {
35 	u64 start, end;
36 	start = trace_clock_local();
37 	do {
38 		end = trace_clock_local();
39 		if (kthread_should_stop())
40 			break;
41 	} while ((end - start) < (time * 1000));
42 }
43 
44 static __always_inline void irqoff_test(void)
45 {
46 	unsigned long flags;
47 	local_irq_save(flags);
48 	busy_wait(delay);
49 	local_irq_restore(flags);
50 }
51 
52 static __always_inline void preemptoff_test(void)
53 {
54 	preempt_disable();
55 	busy_wait(delay);
56 	preempt_enable();
57 }
58 
59 static void execute_preemptirqtest(int idx)
60 {
61 	if (!strcmp(test_mode, "irq"))
62 		irqoff_test();
63 	else if (!strcmp(test_mode, "preempt"))
64 		preemptoff_test();
65 	else if (!strcmp(test_mode, "alternate")) {
66 		if (idx % 2 == 0)
67 			irqoff_test();
68 		else
69 			preemptoff_test();
70 	}
71 }
72 
73 #define DECLARE_TESTFN(POSTFIX)				\
74 	static void preemptirqtest_##POSTFIX(int idx)	\
75 	{						\
76 		execute_preemptirqtest(idx);		\
77 	}						\
78 
79 /*
80  * We create 10 different functions, so that we can get 10 different
81  * backtraces.
82  */
83 DECLARE_TESTFN(0)
84 DECLARE_TESTFN(1)
85 DECLARE_TESTFN(2)
86 DECLARE_TESTFN(3)
87 DECLARE_TESTFN(4)
88 DECLARE_TESTFN(5)
89 DECLARE_TESTFN(6)
90 DECLARE_TESTFN(7)
91 DECLARE_TESTFN(8)
92 DECLARE_TESTFN(9)
93 
94 static void (*testfuncs[])(int)  = {
95 	preemptirqtest_0,
96 	preemptirqtest_1,
97 	preemptirqtest_2,
98 	preemptirqtest_3,
99 	preemptirqtest_4,
100 	preemptirqtest_5,
101 	preemptirqtest_6,
102 	preemptirqtest_7,
103 	preemptirqtest_8,
104 	preemptirqtest_9,
105 };
106 
107 #define NR_TEST_FUNCS ARRAY_SIZE(testfuncs)
108 
109 static int preemptirq_delay_run(void *data)
110 {
111 	int i;
112 	int s = MIN(burst_size, NR_TEST_FUNCS);
113 
114 	for (i = 0; i < s; i++)
115 		(testfuncs[i])(i);
116 	return 0;
117 }
118 
119 static struct task_struct *preemptirq_start_test(void)
120 {
121 	char task_name[50];
122 
123 	snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
124 	return kthread_run(preemptirq_delay_run, NULL, task_name);
125 }
126 
127 
128 static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr,
129 			 const char *buf, size_t count)
130 {
131 	preemptirq_start_test();
132 	return count;
133 }
134 
135 static struct kobj_attribute trigger_attribute =
136 	__ATTR(trigger, 0200, NULL, trigger_store);
137 
138 static struct attribute *attrs[] = {
139 	&trigger_attribute.attr,
140 	NULL,
141 };
142 
143 static struct attribute_group attr_group = {
144 	.attrs = attrs,
145 };
146 
147 static struct kobject *preemptirq_delay_kobj;
148 
149 static int __init preemptirq_delay_init(void)
150 {
151 	struct task_struct *test_task;
152 	int retval;
153 
154 	test_task = preemptirq_start_test();
155 	retval = PTR_ERR_OR_ZERO(test_task);
156 	if (retval != 0)
157 		return retval;
158 
159 	preemptirq_delay_kobj = kobject_create_and_add("preemptirq_delay_test",
160 						       kernel_kobj);
161 	if (!preemptirq_delay_kobj)
162 		return -ENOMEM;
163 
164 	retval = sysfs_create_group(preemptirq_delay_kobj, &attr_group);
165 	if (retval)
166 		kobject_put(preemptirq_delay_kobj);
167 
168 	return retval;
169 }
170 
171 static void __exit preemptirq_delay_exit(void)
172 {
173 	kobject_put(preemptirq_delay_kobj);
174 }
175 
176 module_init(preemptirq_delay_init)
177 module_exit(preemptirq_delay_exit)
178 MODULE_LICENSE("GPL v2");
179