linux/kernel/latencytop.c at master · fabgithub/linux · GitHub

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* latencytop.c: Latency display infrastructure

* 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);

linux/kernel/latencytop.c at master · fabgithub/linux · GitHub

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