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b886d83c | 1 | // SPDX-License-Identifier: GPL-2.0-only |
9745512c AV |
2 | /* |
3 | * latencytop.c: Latency display infrastructure | |
4 | * | |
5 | * (C) Copyright 2008 Intel Corporation | |
6 | * Author: Arjan van de Ven <arjan@linux.intel.com> | |
9745512c | 7 | */ |
ad0b0fd5 AV |
8 | |
9 | /* | |
10 | * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is | |
11 | * used by the "latencytop" userspace tool. The latency that is tracked is not | |
12 | * the 'traditional' interrupt latency (which is primarily caused by something | |
13 | * else consuming CPU), but instead, it is the latency an application encounters | |
14 | * because the kernel sleeps on its behalf for various reasons. | |
15 | * | |
16 | * This code tracks 2 levels of statistics: | |
17 | * 1) System level latency | |
18 | * 2) Per process latency | |
19 | * | |
20 | * The latency is stored in fixed sized data structures in an accumulated form; | |
21 | * if the "same" latency cause is hit twice, this will be tracked as one entry | |
22 | * in the data structure. Both the count, total accumulated latency and maximum | |
23 | * latency are tracked in this data structure. When the fixed size structure is | |
24 | * full, no new causes are tracked until the buffer is flushed by writing to | |
25 | * the /proc file; the userspace tool does this on a regular basis. | |
26 | * | |
27 | * A latency cause is identified by a stringified backtrace at the point that | |
28 | * the scheduler gets invoked. The userland tool will use this string to | |
29 | * identify the cause of the latency in human readable form. | |
30 | * | |
31 | * The information is exported via /proc/latency_stats and /proc/<pid>/latency. | |
32 | * These files look like this: | |
33 | * | |
34 | * Latency Top version : v0.1 | |
35 | * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl | |
36 | * | | | | | |
37 | * | | | +----> the stringified backtrace | |
38 | * | | +---------> The maximum latency for this entry in microseconds | |
39 | * | +--------------> The accumulated latency for this entry (microseconds) | |
40 | * +-------------------> The number of times this entry is hit | |
41 | * | |
42 | * (note: the average latency is the accumulated latency divided by the number | |
43 | * of times) | |
44 | */ | |
45 | ||
9745512c AV |
46 | #include <linux/kallsyms.h> |
47 | #include <linux/seq_file.h> | |
48 | #include <linux/notifier.h> | |
49 | #include <linux/spinlock.h> | |
50 | #include <linux/proc_fs.h> | |
cb251765 | 51 | #include <linux/latencytop.h> |
9984de1a | 52 | #include <linux/export.h> |
9745512c | 53 | #include <linux/sched.h> |
b17b0153 | 54 | #include <linux/sched/debug.h> |
3905f9ad | 55 | #include <linux/sched/stat.h> |
9745512c | 56 | #include <linux/list.h> |
9745512c | 57 | #include <linux/stacktrace.h> |
988f11e0 | 58 | #include <linux/sysctl.h> |
9745512c | 59 | |
757455d4 | 60 | static DEFINE_RAW_SPINLOCK(latency_lock); |
9745512c AV |
61 | |
62 | #define MAXLR 128 | |
63 | static struct latency_record latency_record[MAXLR]; | |
64 | ||
65 | int latencytop_enabled; | |
66 | ||
988f11e0 | 67 | #ifdef CONFIG_SYSCTL |
68 | static int sysctl_latencytop(struct ctl_table *table, int write, void *buffer, | |
69 | size_t *lenp, loff_t *ppos) | |
70 | { | |
71 | int err; | |
72 | ||
73 | err = proc_dointvec(table, write, buffer, lenp, ppos); | |
74 | if (latencytop_enabled) | |
75 | force_schedstat_enabled(); | |
76 | ||
77 | return err; | |
78 | } | |
79 | ||
80 | static struct ctl_table latencytop_sysctl[] = { | |
81 | { | |
82 | .procname = "latencytop", | |
83 | .data = &latencytop_enabled, | |
84 | .maxlen = sizeof(int), | |
85 | .mode = 0644, | |
86 | .proc_handler = sysctl_latencytop, | |
87 | }, | |
988f11e0 | 88 | }; |
89 | #endif | |
90 | ||
e02c9b0d | 91 | void clear_tsk_latency_tracing(struct task_struct *p) |
9745512c AV |
92 | { |
93 | unsigned long flags; | |
94 | ||
757455d4 | 95 | raw_spin_lock_irqsave(&latency_lock, flags); |
9745512c AV |
96 | memset(&p->latency_record, 0, sizeof(p->latency_record)); |
97 | p->latency_record_count = 0; | |
757455d4 | 98 | raw_spin_unlock_irqrestore(&latency_lock, flags); |
9745512c AV |
99 | } |
100 | ||
101 | static void clear_global_latency_tracing(void) | |
102 | { | |
103 | unsigned long flags; | |
104 | ||
757455d4 | 105 | raw_spin_lock_irqsave(&latency_lock, flags); |
9745512c | 106 | memset(&latency_record, 0, sizeof(latency_record)); |
757455d4 | 107 | raw_spin_unlock_irqrestore(&latency_lock, flags); |
9745512c AV |
108 | } |
109 | ||
110 | static void __sched | |
eaa1809b FF |
111 | account_global_scheduler_latency(struct task_struct *tsk, |
112 | struct latency_record *lat) | |
9745512c | 113 | { |
b8147511 | 114 | int firstnonnull = MAXLR; |
9745512c AV |
115 | int i; |
116 | ||
9745512c AV |
117 | /* skip kernel threads for now */ |
118 | if (!tsk->mm) | |
119 | return; | |
120 | ||
121 | for (i = 0; i < MAXLR; i++) { | |
19fb518c DA |
122 | int q, same = 1; |
123 | ||
9745512c AV |
124 | /* Nothing stored: */ |
125 | if (!latency_record[i].backtrace[0]) { | |
126 | if (firstnonnull > i) | |
127 | firstnonnull = i; | |
128 | continue; | |
129 | } | |
ad0b0fd5 | 130 | for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
19fb518c DA |
131 | unsigned long record = lat->backtrace[q]; |
132 | ||
133 | if (latency_record[i].backtrace[q] != record) { | |
9745512c | 134 | same = 0; |
9745512c | 135 | break; |
19fb518c DA |
136 | } |
137 | ||
accddc41 TG |
138 | /* 0 entry marks end of backtrace: */ |
139 | if (!record) | |
9745512c AV |
140 | break; |
141 | } | |
142 | if (same) { | |
143 | latency_record[i].count++; | |
144 | latency_record[i].time += lat->time; | |
145 | if (lat->time > latency_record[i].max) | |
146 | latency_record[i].max = lat->time; | |
147 | return; | |
148 | } | |
149 | } | |
150 | ||
151 | i = firstnonnull; | |
b8147511 | 152 | if (i >= MAXLR) |
9745512c AV |
153 | return; |
154 | ||
155 | /* Allocted a new one: */ | |
156 | memcpy(&latency_record[i], lat, sizeof(struct latency_record)); | |
157 | } | |
158 | ||
ad0b0fd5 | 159 | /** |
25985edc | 160 | * __account_scheduler_latency - record an occurred latency |
ad0b0fd5 AV |
161 | * @tsk - the task struct of the task hitting the latency |
162 | * @usecs - the duration of the latency in microseconds | |
163 | * @inter - 1 if the sleep was interruptible, 0 if uninterruptible | |
164 | * | |
165 | * This function is the main entry point for recording latency entries | |
166 | * as called by the scheduler. | |
167 | * | |
168 | * This function has a few special cases to deal with normal 'non-latency' | |
169 | * sleeps: specifically, interruptible sleep longer than 5 msec is skipped | |
170 | * since this usually is caused by waiting for events via select() and co. | |
171 | * | |
172 | * Negative latencies (caused by time going backwards) are also explicitly | |
173 | * skipped. | |
174 | */ | |
9745512c | 175 | void __sched |
ad0b0fd5 | 176 | __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter) |
9745512c AV |
177 | { |
178 | unsigned long flags; | |
179 | int i, q; | |
180 | struct latency_record lat; | |
181 | ||
9745512c AV |
182 | /* Long interruptible waits are generally user requested... */ |
183 | if (inter && usecs > 5000) | |
184 | return; | |
185 | ||
ad0b0fd5 AV |
186 | /* Negative sleeps are time going backwards */ |
187 | /* Zero-time sleeps are non-interesting */ | |
188 | if (usecs <= 0) | |
189 | return; | |
190 | ||
9745512c AV |
191 | memset(&lat, 0, sizeof(lat)); |
192 | lat.count = 1; | |
193 | lat.time = usecs; | |
194 | lat.max = usecs; | |
f9387721 TG |
195 | |
196 | stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0); | |
9745512c | 197 | |
757455d4 | 198 | raw_spin_lock_irqsave(&latency_lock, flags); |
9745512c AV |
199 | |
200 | account_global_scheduler_latency(tsk, &lat); | |
201 | ||
38715258 | 202 | for (i = 0; i < tsk->latency_record_count; i++) { |
9745512c AV |
203 | struct latency_record *mylat; |
204 | int same = 1; | |
19fb518c | 205 | |
9745512c | 206 | mylat = &tsk->latency_record[i]; |
ad0b0fd5 | 207 | for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
19fb518c DA |
208 | unsigned long record = lat.backtrace[q]; |
209 | ||
210 | if (mylat->backtrace[q] != record) { | |
9745512c | 211 | same = 0; |
9745512c | 212 | break; |
19fb518c DA |
213 | } |
214 | ||
accddc41 TG |
215 | /* 0 entry is end of backtrace */ |
216 | if (!record) | |
9745512c AV |
217 | break; |
218 | } | |
219 | if (same) { | |
220 | mylat->count++; | |
221 | mylat->time += lat.time; | |
222 | if (lat.time > mylat->max) | |
223 | mylat->max = lat.time; | |
224 | goto out_unlock; | |
225 | } | |
226 | } | |
227 | ||
38715258 KC |
228 | /* |
229 | * short term hack; if we're > 32 we stop; future we recycle: | |
230 | */ | |
231 | if (tsk->latency_record_count >= LT_SAVECOUNT) | |
232 | goto out_unlock; | |
233 | ||
9745512c | 234 | /* Allocated a new one: */ |
38715258 | 235 | i = tsk->latency_record_count++; |
9745512c AV |
236 | memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); |
237 | ||
238 | out_unlock: | |
757455d4 | 239 | raw_spin_unlock_irqrestore(&latency_lock, flags); |
9745512c AV |
240 | } |
241 | ||
242 | static int lstats_show(struct seq_file *m, void *v) | |
243 | { | |
244 | int i; | |
245 | ||
246 | seq_puts(m, "Latency Top version : v0.1\n"); | |
247 | ||
248 | for (i = 0; i < MAXLR; i++) { | |
34e49d4f JP |
249 | struct latency_record *lr = &latency_record[i]; |
250 | ||
251 | if (lr->backtrace[0]) { | |
9745512c | 252 | int q; |
34e49d4f JP |
253 | seq_printf(m, "%i %lu %lu", |
254 | lr->count, lr->time, lr->max); | |
9745512c | 255 | for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
34e49d4f | 256 | unsigned long bt = lr->backtrace[q]; |
accddc41 | 257 | |
34e49d4f | 258 | if (!bt) |
9745512c | 259 | break; |
accddc41 | 260 | |
34e49d4f | 261 | seq_printf(m, " %ps", (void *)bt); |
9745512c | 262 | } |
eaa1809b | 263 | seq_puts(m, "\n"); |
9745512c AV |
264 | } |
265 | } | |
266 | return 0; | |
267 | } | |
268 | ||
269 | static ssize_t | |
270 | lstats_write(struct file *file, const char __user *buf, size_t count, | |
271 | loff_t *offs) | |
272 | { | |
273 | clear_global_latency_tracing(); | |
274 | ||
275 | return count; | |
276 | } | |
277 | ||
278 | static int lstats_open(struct inode *inode, struct file *filp) | |
279 | { | |
280 | return single_open(filp, lstats_show, NULL); | |
281 | } | |
282 | ||
97a32539 AD |
283 | static const struct proc_ops lstats_proc_ops = { |
284 | .proc_open = lstats_open, | |
285 | .proc_read = seq_read, | |
286 | .proc_write = lstats_write, | |
287 | .proc_lseek = seq_lseek, | |
288 | .proc_release = single_release, | |
9745512c AV |
289 | }; |
290 | ||
291 | static int __init init_lstats_procfs(void) | |
292 | { | |
97a32539 | 293 | proc_create("latency_stats", 0644, NULL, &lstats_proc_ops); |
988f11e0 | 294 | #ifdef CONFIG_SYSCTL |
295 | register_sysctl_init("kernel", latencytop_sysctl); | |
296 | #endif | |
9745512c AV |
297 | return 0; |
298 | } | |
ad0b0fd5 | 299 | device_initcall(init_lstats_procfs); |