1 // SPDX-License-Identifier: GPL-2.0-only 1
2 /*
3 * latencytop.c: Latency display infrastructur
4 *
5 * (C) Copyright 2008 Intel Corporation
6 * Author: Arjan van de Ven <arjan@linux.intel
7 */
8
9 /*
10 * CONFIG_LATENCYTOP enables a kernel latency
11 * used by the "latencytop" userspace tool. Th
12 * the 'traditional' interrupt latency (which
13 * else consuming CPU), but instead, it is the
14 * because the kernel sleeps on its behalf for
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 s
21 * if the "same" latency cause is hit twice, t
22 * in the data structure. Both the count, tota
23 * latency are tracked in this data structure.
24 * full, no new causes are tracked until the b
25 * the /proc file; the userspace tool does thi
26 *
27 * A latency cause is identified by a stringif
28 * the scheduler gets invoked. The userland to
29 * identify the cause of the latency in human
30 *
31 * The information is exported via /proc/laten
32 * These files look like this:
33 *
34 * Latency Top version : v0.1
35 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_i
36 * | | | |
37 * | | | +----> the stringified backt
38 * | | +---------> The maximum latency f
39 * | +--------------> The accumulated laten
40 * +-------------------> The number of times t
41 *
42 * (note: the average latency is the accumulat
43 * of times)
44 */
45
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>
51 #include <linux/latencytop.h>
52 #include <linux/export.h>
53 #include <linux/sched.h>
54 #include <linux/sched/debug.h>
55 #include <linux/sched/stat.h>
56 #include <linux/list.h>
57 #include <linux/stacktrace.h>
58 #include <linux/sysctl.h>
59
60 static DEFINE_RAW_SPINLOCK(latency_lock);
61
62 #define MAXLR 128
63 static struct latency_record latency_record[MA
64
65 int latencytop_enabled;
66
67 #ifdef CONFIG_SYSCTL
68 static int sysctl_latencytop(const struct ctl_
69 size_t *lenp, loff_t *ppos)
70 {
71 int err;
72
73 err = proc_dointvec(table, write, buff
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_enab
84 .maxlen = sizeof(int),
85 .mode = 0644,
86 .proc_handler = sysctl_laten
87 },
88 };
89 #endif
90
91 void clear_tsk_latency_tracing(struct task_str
92 {
93 unsigned long flags;
94
95 raw_spin_lock_irqsave(&latency_lock, f
96 memset(&p->latency_record, 0, sizeof(p
97 p->latency_record_count = 0;
98 raw_spin_unlock_irqrestore(&latency_lo
99 }
100
101 static void clear_global_latency_tracing(void)
102 {
103 unsigned long flags;
104
105 raw_spin_lock_irqsave(&latency_lock, f
106 memset(&latency_record, 0, sizeof(late
107 raw_spin_unlock_irqrestore(&latency_lo
108 }
109
110 static void __sched
111 account_global_scheduler_latency(struct task_s
112 struct latenc
113 {
114 int firstnonnull = MAXLR;
115 int i;
116
117 /* skip kernel threads for now */
118 if (!tsk->mm)
119 return;
120
121 for (i = 0; i < MAXLR; i++) {
122 int q, same = 1;
123
124 /* Nothing stored: */
125 if (!latency_record[i].backtra
126 if (firstnonnull > i)
127 firstnonnull =
128 continue;
129 }
130 for (q = 0; q < LT_BACKTRACEDE
131 unsigned long record =
132
133 if (latency_record[i].
134 same = 0;
135 break;
136 }
137
138 /* 0 entry marks end o
139 if (!record)
140 break;
141 }
142 if (same) {
143 latency_record[i].coun
144 latency_record[i].time
145 if (lat->time > latenc
146 latency_record
147 return;
148 }
149 }
150
151 i = firstnonnull;
152 if (i >= MAXLR)
153 return;
154
155 /* Allocted a new one: */
156 memcpy(&latency_record[i], lat, sizeof
157 }
158
159 /**
160 * __account_scheduler_latency - record an occ
161 * @tsk - the task struct of the task hitting
162 * @usecs - the duration of the latency in mic
163 * @inter - 1 if the sleep was interruptible,
164 *
165 * This function is the main entry point for r
166 * as called by the scheduler.
167 *
168 * This function has a few special cases to de
169 * sleeps: specifically, interruptible sleep l
170 * since this usually is caused by waiting for
171 *
172 * Negative latencies (caused by time going ba
173 * skipped.
174 */
175 void __sched
176 __account_scheduler_latency(struct task_struct
177 {
178 unsigned long flags;
179 int i, q;
180 struct latency_record lat;
181
182 /* Long interruptible waits are genera
183 if (inter && usecs > 5000)
184 return;
185
186 /* Negative sleeps are time going back
187 /* Zero-time sleeps are non-interestin
188 if (usecs <= 0)
189 return;
190
191 memset(&lat, 0, sizeof(lat));
192 lat.count = 1;
193 lat.time = usecs;
194 lat.max = usecs;
195
196 stack_trace_save_tsk(tsk, lat.backtrac
197
198 raw_spin_lock_irqsave(&latency_lock, f
199
200 account_global_scheduler_latency(tsk,
201
202 for (i = 0; i < tsk->latency_record_co
203 struct latency_record *mylat;
204 int same = 1;
205
206 mylat = &tsk->latency_record[i
207 for (q = 0; q < LT_BACKTRACEDE
208 unsigned long record =
209
210 if (mylat->backtrace[q
211 same = 0;
212 break;
213 }
214
215 /* 0 entry is end of b
216 if (!record)
217 break;
218 }
219 if (same) {
220 mylat->count++;
221 mylat->time += lat.tim
222 if (lat.time > mylat->
223 mylat->max = l
224 goto out_unlock;
225 }
226 }
227
228 /*
229 * short term hack; if we're > 32 we s
230 */
231 if (tsk->latency_record_count >= LT_SA
232 goto out_unlock;
233
234 /* Allocated a new one: */
235 i = tsk->latency_record_count++;
236 memcpy(&tsk->latency_record[i], &lat,
237
238 out_unlock:
239 raw_spin_unlock_irqrestore(&latency_lo
240 }
241
242 static int lstats_show(struct seq_file *m, voi
243 {
244 int i;
245
246 seq_puts(m, "Latency Top version : v0.
247
248 for (i = 0; i < MAXLR; i++) {
249 struct latency_record *lr = &l
250
251 if (lr->backtrace[0]) {
252 int q;
253 seq_printf(m, "%i %lu
254 lr->count,
255 for (q = 0; q < LT_BAC
256 unsigned long
257
258 if (!bt)
259 break;
260
261 seq_printf(m,
262 }
263 seq_puts(m, "\n");
264 }
265 }
266 return 0;
267 }
268
269 static ssize_t
270 lstats_write(struct file *file, const char __u
271 loff_t *offs)
272 {
273 clear_global_latency_tracing();
274
275 return count;
276 }
277
278 static int lstats_open(struct inode *inode, st
279 {
280 return single_open(filp, lstats_show,
281 }
282
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,
289 };
290
291 static int __init init_lstats_procfs(void)
292 {
293 proc_create("latency_stats", 0644, NUL
294 #ifdef CONFIG_SYSCTL
295 register_sysctl_init("kernel", latency
296 #endif
297 return 0;
298 }
299 device_initcall(init_lstats_procfs);
300
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