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/*
* 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 128
static 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 __sched
account_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_t
lstats_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);
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