/* * latencytop.c: Latency display infrastructure * * (C) Copyright 2008 Intel Corporation * Author: Arjan van de Ven <arjan@linux.intel.com> * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; version 2 * of the License. */ /* * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is * used by the "latencytop" userspace tool. The latency that is tracked is not * the 'traditional' interrupt latency (which is primarily caused by something * else consuming CPU), but instead, it is the latency an application encounters * because the kernel sleeps on its behalf for various reasons. * * This code tracks 2 levels of statistics: * 1) System level latency * 2) Per process latency * * The latency is stored in fixed sized data structures in an accumulated form; * if the "same" latency cause is hit twice, this will be tracked as one entry * in the data structure. Both the count, total accumulated latency and maximum * latency are tracked in this data structure. When the fixed size structure is * full, no new causes are tracked until the buffer is flushed by writing to * the /proc file; the userspace tool does this on a regular basis. * * A latency cause is identified by a stringified backtrace at the point that * the scheduler gets invoked. The userland tool will use this string to * identify the cause of the latency in human readable form. * * The information is exported via /proc/latency_stats and /proc/<pid>/latency. * These files look like this: * * Latency Top version : v0.1 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl * |    |    |    | * |    |    |    +----> the stringified backtrace * |    |    +---------> The maximum latency for this entry in microseconds * |    +--------------> The accumulated latency for this entry (microseconds) * +-------------------> The number of times this entry is hit * * (note: the average latency is the accumulated latency divided by the number * of times) */ #include <linux/latencytop.h>#include <linux/kallsyms.h>#include <linux/seq_file.h>#include <linux/notifier.h>#include <linux/spinlock.h>#include <linux/proc_fs.h>#include <linux/export.h>#include <linux/sched.h>#include <linux/list.h>#include <linux/stacktrace.h> static DEFINE_RAW_SPINLOCK(latency_lock); #define MAXLR 128static struct latency_record latency_record[MAXLR]; int latencytop_enabled; void clear_all_latency_tracing(struct task_struct *p){	unsigned long flags; 	if (!latencytop_enabled)		return; 	raw_spin_lock_irqsave(&latency_lock, flags);	memset(&p->latency_record, 0, sizeof(p->latency_record));	p->latency_record_count = 0;	raw_spin_unlock_irqrestore(&latency_lock, flags);} static void clear_global_latency_tracing(void){	unsigned long flags; 	raw_spin_lock_irqsave(&latency_lock, flags);	memset(&latency_record, 0, sizeof(latency_record));	raw_spin_unlock_irqrestore(&latency_lock, flags);} static void __schedaccount_global_scheduler_latency(struct task_struct *tsk, struct latency_record *lat){	int firstnonnull = MAXLR + 1;	int i; 	if (!latencytop_enabled)		return; 	/* skip kernel threads for now */	if (!tsk->mm)		return; 	for (i = 0; i < MAXLR; i++) {		int q, same = 1; 		/* Nothing stored: */		if (!latency_record[i].backtrace[0]) {			if (firstnonnull > i)				firstnonnull = i;			continue;		}		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {			unsigned long record = lat->backtrace[q]; 			if (latency_record[i].backtrace[q] != record) {				same = 0;				break;			} 			/* 0 and ULONG_MAX entries mean end of backtrace: */			if (record == 0 || record == ULONG_MAX)				break;		}		if (same) {			latency_record[i].count++;			latency_record[i].time += lat->time;			if (lat->time > latency_record[i].max)				latency_record[i].max = lat->time;			return;		}	} 	i = firstnonnull;	if (i >= MAXLR - 1)		return; 	/* Allocted a new one: */	memcpy(&latency_record[i], lat, sizeof(struct latency_record));} /* * Iterator to store a backtrace into a latency record entry */static inline void store_stacktrace(struct task_struct *tsk,					struct latency_record *lat){	struct stack_trace trace; 	memset(&trace, 0, sizeof(trace));	trace.max_entries = LT_BACKTRACEDEPTH;	trace.entries = &lat->backtrace[0];	save_stack_trace_tsk(tsk, &trace);} /** * __account_scheduler_latency - record an occurred latency * @tsk - the task struct of the task hitting the latency * @usecs - the duration of the latency in microseconds * @inter - 1 if the sleep was interruptible, 0 if uninterruptible * * This function is the main entry point for recording latency entries * as called by the scheduler. * * This function has a few special cases to deal with normal 'non-latency' * sleeps: specifically, interruptible sleep longer than 5 msec is skipped * since this usually is caused by waiting for events via select() and co. * * Negative latencies (caused by time going backwards) are also explicitly * skipped. */void __sched__account_scheduler_latency(struct task_struct *tsk, int usecs, int inter){	unsigned long flags;	int i, q;	struct latency_record lat; 	/* Long interruptible waits are generally user requested... */	if (inter && usecs > 5000)		return; 	/* Negative sleeps are time going backwards */	/* Zero-time sleeps are non-interesting */	if (usecs <= 0)		return; 	memset(&lat, 0, sizeof(lat));	lat.count = 1;	lat.time = usecs;	lat.max = usecs;	store_stacktrace(tsk, &lat); 	raw_spin_lock_irqsave(&latency_lock, flags); 	account_global_scheduler_latency(tsk, &lat); 	for (i = 0; i < tsk->latency_record_count; i++) {		struct latency_record *mylat;		int same = 1; 		mylat = &tsk->latency_record[i];		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {			unsigned long record = lat.backtrace[q]; 			if (mylat->backtrace[q] != record) {				same = 0;				break;			} 			/* 0 and ULONG_MAX entries mean end of backtrace: */			if (record == 0 || record == ULONG_MAX)				break;		}		if (same) {			mylat->count++;			mylat->time += lat.time;			if (lat.time > mylat->max)				mylat->max = lat.time;			goto out_unlock;		}	} 	/*	 * short term hack; if we're > 32 we stop; future we recycle:	 */	if (tsk->latency_record_count >= LT_SAVECOUNT)		goto out_unlock; 	/* Allocated a new one: */	i = tsk->latency_record_count++;	memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); out_unlock:	raw_spin_unlock_irqrestore(&latency_lock, flags);} static int lstats_show(struct seq_file *m, void *v){	int i; 	seq_puts(m, "Latency Top version : v0.1\n"); 	for (i = 0; i < MAXLR; i++) {		struct latency_record *lr = &latency_record[i]; 		if (lr->backtrace[0]) {			int q;			seq_printf(m, "%i %lu %lu",				   lr->count, lr->time, lr->max);			for (q = 0; q < LT_BACKTRACEDEPTH; q++) {				unsigned long bt = lr->backtrace[q];				if (!bt)					break;				if (bt == ULONG_MAX)					break;				seq_printf(m, " %ps", (void *)bt);			}			seq_printf(m, "\n");		}	}	return 0;} static ssize_tlstats_write(struct file *file, const char __user *buf, size_t count,	     loff_t *offs){	clear_global_latency_tracing(); 	return count;} static int lstats_open(struct inode *inode, struct file *filp){	return single_open(filp, lstats_show, NULL);} static const struct file_operations lstats_fops = {	.open		= lstats_open,	.read		= seq_read,	.write		= lstats_write,	.llseek		= seq_lseek,	.release	= single_release,}; static int __init init_lstats_procfs(void){	proc_create("latency_stats", 0644, NULL, &lstats_fops);	return 0;}device_initcall(init_lstats_procfs);