linux/kernel/latencytop.c

1 // SPDX-License-Identifier: GPL-2.0-only
3  * latencytop.c: Latency display infrastructure
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
17  * 1) System level latency
18  * 2) Per process latency
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
27  * A latency cause is identified by a stringified backtrace at the point that
29  * identify the cause of the latency in human readable form.
31  * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
34  * Latency Top version : v0.1
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
42  * (note: the average latency is the accumulated latency divided by the number
97 	memset(&p->latency_record, 0, sizeof(p->latency_record));  in clear_tsk_latency_tracing()
98 	p->latency_record_count = 0;  in clear_tsk_latency_tracing()
119 	if (!tsk->mm)  in account_global_scheduler_latency()
132 			unsigned long record = lat->backtrace[q];  in account_global_scheduler_latency()
139 			/* 0 entry marks end of backtrace: */  in account_global_scheduler_latency()
145 			latency_record[i].time += lat->time;  in account_global_scheduler_latency()
146 			if (lat->time > latency_record[i].max)  in account_global_scheduler_latency()
147 				latency_record[i].max = lat->time;  in account_global_scheduler_latency()
161  * __account_scheduler_latency - record an occurred latency
162  * @tsk - the task struct of the task hitting the latency
163  * @usecs - the duration of the latency in microseconds
164  * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
166  * This function is the main entry point for recording latency entries
169  * This function has a few special cases to deal with normal 'non-latency'
188 	/* Zero-time sleeps are non-interesting */  in __account_scheduler_latency()
203 	for (i = 0; i < tsk->latency_record_count; i++) {  in __account_scheduler_latency()
207 		mylat = &tsk->latency_record[i];  in __account_scheduler_latency()
211 			if (mylat->backtrace[q] != record) {  in __account_scheduler_latency()
216 			/* 0 entry is end of backtrace */  in __account_scheduler_latency()
221 			mylat->count++;  in __account_scheduler_latency()
222 			mylat->time += lat.time;  in __account_scheduler_latency()
223 			if (lat.time > mylat->max)  in __account_scheduler_latency()
224 				mylat->max = lat.time;  in __account_scheduler_latency()
232 	if (tsk->latency_record_count >= LT_SAVECOUNT)  in __account_scheduler_latency()
236 	i = tsk->latency_record_count++;  in __account_scheduler_latency()
237 	memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));  in __account_scheduler_latency()
247 	seq_puts(m, "Latency Top version : v0.1\n");  in lstats_show()
252 		if (lr->backtrace[0]) {  in lstats_show()
255 				   lr->count, lr->time, lr->max);  in lstats_show()
257 				unsigned long bt = lr->backtrace[q];  in lstats_show()