1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * latencytop.c: Latency display infrastructure
4 *
5 * (C) Copyright 2008 Intel Corporation
6 * Author: Arjan van de Ven <arjan@linux.intel.com>
7 */
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
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
59 static DEFINE_RAW_SPINLOCK(latency_lock);
60
61 #define MAXLR 128
62 static struct latency_record latency_record[MAXLR];
63
64 int latencytop_enabled;
65
clear_tsk_latency_tracing(struct task_struct * p)66 void clear_tsk_latency_tracing(struct task_struct *p)
67 {
68 unsigned long flags;
69
70 raw_spin_lock_irqsave(&latency_lock, flags);
71 memset(&p->latency_record, 0, sizeof(p->latency_record));
72 p->latency_record_count = 0;
73 raw_spin_unlock_irqrestore(&latency_lock, flags);
74 }
75
clear_global_latency_tracing(void)76 static void clear_global_latency_tracing(void)
77 {
78 unsigned long flags;
79
80 raw_spin_lock_irqsave(&latency_lock, flags);
81 memset(&latency_record, 0, sizeof(latency_record));
82 raw_spin_unlock_irqrestore(&latency_lock, flags);
83 }
84
85 static void __sched
account_global_scheduler_latency(struct task_struct * tsk,struct latency_record * lat)86 account_global_scheduler_latency(struct task_struct *tsk,
87 struct latency_record *lat)
88 {
89 int firstnonnull = MAXLR + 1;
90 int i;
91
92 /* skip kernel threads for now */
93 if (!tsk->mm)
94 return;
95
96 for (i = 0; i < MAXLR; i++) {
97 int q, same = 1;
98
99 /* Nothing stored: */
100 if (!latency_record[i].backtrace[0]) {
101 if (firstnonnull > i)
102 firstnonnull = i;
103 continue;
104 }
105 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
106 unsigned long record = lat->backtrace[q];
107
108 if (latency_record[i].backtrace[q] != record) {
109 same = 0;
110 break;
111 }
112
113 /* 0 entry marks end of backtrace: */
114 if (!record)
115 break;
116 }
117 if (same) {
118 latency_record[i].count++;
119 latency_record[i].time += lat->time;
120 if (lat->time > latency_record[i].max)
121 latency_record[i].max = lat->time;
122 return;
123 }
124 }
125
126 i = firstnonnull;
127 if (i >= MAXLR - 1)
128 return;
129
130 /* Allocted a new one: */
131 memcpy(&latency_record[i], lat, sizeof(struct latency_record));
132 }
133
134 /**
135 * __account_scheduler_latency - record an occurred latency
136 * @tsk - the task struct of the task hitting the latency
137 * @usecs - the duration of the latency in microseconds
138 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
139 *
140 * This function is the main entry point for recording latency entries
141 * as called by the scheduler.
142 *
143 * This function has a few special cases to deal with normal 'non-latency'
144 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
145 * since this usually is caused by waiting for events via select() and co.
146 *
147 * Negative latencies (caused by time going backwards) are also explicitly
148 * skipped.
149 */
150 void __sched
__account_scheduler_latency(struct task_struct * tsk,int usecs,int inter)151 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
152 {
153 unsigned long flags;
154 int i, q;
155 struct latency_record lat;
156
157 /* Long interruptible waits are generally user requested... */
158 if (inter && usecs > 5000)
159 return;
160
161 /* Negative sleeps are time going backwards */
162 /* Zero-time sleeps are non-interesting */
163 if (usecs <= 0)
164 return;
165
166 memset(&lat, 0, sizeof(lat));
167 lat.count = 1;
168 lat.time = usecs;
169 lat.max = usecs;
170
171 stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0);
172
173 raw_spin_lock_irqsave(&latency_lock, flags);
174
175 account_global_scheduler_latency(tsk, &lat);
176
177 for (i = 0; i < tsk->latency_record_count; i++) {
178 struct latency_record *mylat;
179 int same = 1;
180
181 mylat = &tsk->latency_record[i];
182 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
183 unsigned long record = lat.backtrace[q];
184
185 if (mylat->backtrace[q] != record) {
186 same = 0;
187 break;
188 }
189
190 /* 0 entry is end of backtrace */
191 if (!record)
192 break;
193 }
194 if (same) {
195 mylat->count++;
196 mylat->time += lat.time;
197 if (lat.time > mylat->max)
198 mylat->max = lat.time;
199 goto out_unlock;
200 }
201 }
202
203 /*
204 * short term hack; if we're > 32 we stop; future we recycle:
205 */
206 if (tsk->latency_record_count >= LT_SAVECOUNT)
207 goto out_unlock;
208
209 /* Allocated a new one: */
210 i = tsk->latency_record_count++;
211 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
212
213 out_unlock:
214 raw_spin_unlock_irqrestore(&latency_lock, flags);
215 }
216
lstats_show(struct seq_file * m,void * v)217 static int lstats_show(struct seq_file *m, void *v)
218 {
219 int i;
220
221 seq_puts(m, "Latency Top version : v0.1\n");
222
223 for (i = 0; i < MAXLR; i++) {
224 struct latency_record *lr = &latency_record[i];
225
226 if (lr->backtrace[0]) {
227 int q;
228 seq_printf(m, "%i %lu %lu",
229 lr->count, lr->time, lr->max);
230 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
231 unsigned long bt = lr->backtrace[q];
232
233 if (!bt)
234 break;
235
236 seq_printf(m, " %ps", (void *)bt);
237 }
238 seq_puts(m, "\n");
239 }
240 }
241 return 0;
242 }
243
244 static ssize_t
lstats_write(struct file * file,const char __user * buf,size_t count,loff_t * offs)245 lstats_write(struct file *file, const char __user *buf, size_t count,
246 loff_t *offs)
247 {
248 clear_global_latency_tracing();
249
250 return count;
251 }
252
lstats_open(struct inode * inode,struct file * filp)253 static int lstats_open(struct inode *inode, struct file *filp)
254 {
255 return single_open(filp, lstats_show, NULL);
256 }
257
258 static const struct file_operations lstats_fops = {
259 .open = lstats_open,
260 .read = seq_read,
261 .write = lstats_write,
262 .llseek = seq_lseek,
263 .release = single_release,
264 };
265
init_lstats_procfs(void)266 static int __init init_lstats_procfs(void)
267 {
268 proc_create("latency_stats", 0644, NULL, &lstats_fops);
269 return 0;
270 }
271
sysctl_latencytop(struct ctl_table * table,int write,void __user * buffer,size_t * lenp,loff_t * ppos)272 int sysctl_latencytop(struct ctl_table *table, int write,
273 void __user *buffer, size_t *lenp, loff_t *ppos)
274 {
275 int err;
276
277 err = proc_dointvec(table, write, buffer, lenp, ppos);
278 if (latencytop_enabled)
279 force_schedstat_enabled();
280
281 return err;
282 }
283 device_initcall(init_lstats_procfs);
284
