root/kernel/latencytop.c

DEFINITIONS

1. clear_all_latency_tracing
2. clear_global_latency_tracing
3. account_global_scheduler_latency
4. store_stacktrace
5. account_scheduler_latency
6. lstats_show
7. lstats_write
8. lstats_open
9. init_lstats_procfs

/*
 * 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.
 */
#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/module.h>
#include <linux/sched.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/stacktrace.h>

static DEFINE_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;

        spin_lock_irqsave(&latency_lock, flags);
        memset(&p->latency_record, 0, sizeof(p->latency_record));
        p->latency_record_count = 0;
        spin_unlock_irqrestore(&latency_lock, flags);
}

static void clear_global_latency_tracing(void)
{
        unsigned long flags;

        spin_lock_irqsave(&latency_lock, flags);
        memset(&latency_record, 0, sizeof(latency_record));
        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));
}

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];
        trace.skip = 0;
        save_stack_trace_tsk(tsk, &trace);
}

void __sched
account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
{
        unsigned long flags;
        int i, q;
        struct latency_record lat;

        if (!latencytop_enabled)
                return;

        /* Long interruptible waits are generally user requested... */
        if (inter && usecs > 5000)
                return;

        memset(&lat, 0, sizeof(lat));
        lat.count = 1;
        lat.time = usecs;
        lat.max = usecs;
        store_stacktrace(tsk, &lat);

        spin_lock_irqsave(&latency_lock, flags);

        account_global_scheduler_latency(tsk, &lat);

        /*
         * short term hack; if we're > 32 we stop; future we recycle:
         */
        tsk->latency_record_count++;
        if (tsk->latency_record_count >= LT_SAVECOUNT)
                goto out_unlock;

        for (i = 0; i < LT_SAVECOUNT ; 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;
                }
        }

        /* Allocated a new one: */
        i = tsk->latency_record_count;
        memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));

out_unlock:
        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++) {
                if (latency_record[i].backtrace[0]) {
                        int q;
                        seq_printf(m, "%i %li %li ",
                                latency_record[i].count,
                                latency_record[i].time,
                                latency_record[i].max);
                        for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
                                char sym[KSYM_NAME_LEN];
                                char *c;
                                if (!latency_record[i].backtrace[q])
                                        break;
                                if (latency_record[i].backtrace[q] == ULONG_MAX)
                                        break;
                                sprint_symbol(sym, latency_record[i].backtrace[q]);
                                c = strchr(sym, '+');
                                if (c)
                                        *c = 0;
                                seq_printf(m, "%s ", sym);
                        }
                        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 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;
}
__initcall(init_lstats_procfs);