timer_stats.c

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/*
 * kernel/time/timer_stats.c
 *
 * Collect timer usage statistics.
 *
 * Copyright(C) 2006, Red Hat, Inc., Ingo Molnar
 * Copyright(C) 2006 Timesys Corp., Thomas Gleixner <[email protected]>
 *
 * timer_stats is based on timer_top, a similar functionality which was part of
 * Con Kolivas dyntick patch set. It was developed by Daniel Petrini at the
 * Instituto Nokia de Tecnologia - INdT - Manaus. timer_top's design was based
 * on dynamic allocation of the statistics entries and linear search based
 * lookup combined with a global lock, rather than the static array, hash
 * and per-CPU locking which is used by timer_stats. It was written for the
 * pre hrtimer kernel code and therefore did not take hrtimers into account.
 * Nevertheless it provided the base for the timer_stats implementation and
 * was a helpful source of inspiration. Kudos to Daniel and the Nokia folks
 * for this effort.
 *
 * timer_top.c is
 *  Copyright (C) 2005 Instituto Nokia de Tecnologia - INdT - Manaus
 *  Written by Daniel Petrini <[email protected]>
 *  timer_top.c was released under the GNU General Public License version 2
 *
 * We export the addresses and counting of timer functions being called,
 * the pid and cmdline from the owner process if applicable.
 *
 * Start/stop data collection:
 * # echo [1|0] >/proc/timer_stats
 *
 * Display the information collected so far:
 * # cat /proc/timer_stats
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/proc_fs.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/kallsyms.h>

#include <asm/uaccess.h>

/*
 * This is our basic unit of interest: a timer expiry event identified
 * by the timer, its start/expire functions and the PID of the task that
 * started the timer. We count the number of times an event happens:
 */
struct entry {
    /*
     * Hash list:
     */
    struct entry        *next;

    /*
     * Hash keys:
     */
    void            *timer;
    void            *start_func;
    void            *expire_func;
    pid_t           pid;

    /*
     * Number of timeout events:
     */
    unsigned long       count;
    unsigned int        timer_flag;

    /*
     * We save the command-line string to preserve
     * this information past task exit:
     */
    char            comm[TASK_COMM_LEN + 1];

} ____cacheline_aligned_in_smp;

/*
 * Spinlock protecting the tables - not taken during lookup:
 */
static DEFINE_RAW_SPINLOCK(table_lock);

/*
 * Per-CPU lookup locks for fast hash lookup:
 */
static DEFINE_PER_CPU(raw_spinlock_t, tstats_lookup_lock);

/*
 * Mutex to serialize state changes with show-stats activities:
 */
static DEFINE_MUTEX(show_mutex);

/*
 * Collection status, active/inactive:
 */
int __read_mostly timer_stats_active;

/*
 * Beginning/end timestamps of measurement:
 */
static ktime_t time_start, time_stop;

/*
 * tstat entry structs only get allocated while collection is
 * active and never freed during that time - this simplifies
 * things quite a bit.
 *
 * They get freed when a new collection period is started.
 */
#define MAX_ENTRIES_BITS    10
#define MAX_ENTRIES     (1UL << MAX_ENTRIES_BITS)

static unsigned long nr_entries;
static struct entry entries[MAX_ENTRIES];

static atomic_t overflow_count;

/*
 * The entries are in a hash-table, for fast lookup:
 */
#define TSTAT_HASH_BITS     (MAX_ENTRIES_BITS - 1)
#define TSTAT_HASH_SIZE     (1UL << TSTAT_HASH_BITS)
#define TSTAT_HASH_MASK     (TSTAT_HASH_SIZE - 1)

#define __tstat_hashfn(entry)                       \
    (((unsigned long)(entry)->timer       ^             \
      (unsigned long)(entry)->start_func  ^             \
      (unsigned long)(entry)->expire_func ^             \
      (unsigned long)(entry)->pid       ) & TSTAT_HASH_MASK)

#define tstat_hashentry(entry)  (tstat_hash_table + __tstat_hashfn(entry))

static struct entry *tstat_hash_table[TSTAT_HASH_SIZE] __read_mostly;

static void reset_entries(void)
{
    nr_entries = 0;
    memset(entries, 0, sizeof(entries));
    memset(tstat_hash_table, 0, sizeof(tstat_hash_table));
    atomic_set(&overflow_count, 0);
}

static struct entry *alloc_entry(void)
{
    if (nr_entries >= MAX_ENTRIES)
        return NULL;

    return entries + nr_entries++;
}

static int match_entries(struct entry *entry1, struct entry *entry2)
{
    return entry1->timer       == entry2->timer   &&
           entry1->start_func  == entry2->start_func  &&
           entry1->expire_func == entry2->expire_func &&
           entry1->pid     == entry2->pid;
}

/*
 * Look up whether an entry matching this item is present
 * in the hash already. Must be called with irqs off and the
 * lookup lock held:
 */
static struct entry *tstat_lookup(struct entry *entry, char *comm)
{
    struct entry **head, *curr, *prev;

    head = tstat_hashentry(entry);
    curr = *head;

    /*
     * The fastpath is when the entry is already hashed,
     * we do this with the lookup lock held, but with the
     * table lock not held:
     */
    while (curr) {
        if (match_entries(curr, entry))
            return curr;

        curr = curr->next;
    }
    /*
     * Slowpath: allocate, set up and link a new hash entry:
     */
    prev = NULL;
    curr = *head;

    raw_spin_lock(&table_lock);
    /*
     * Make sure we have not raced with another CPU:
     */
    while (curr) {
        if (match_entries(curr, entry))
            goto out_unlock;

        prev = curr;
        curr = curr->next;
    }

    curr = alloc_entry();
    if (curr) {
        *curr = *entry;
        curr->count = 0;
        curr->next = NULL;
        memcpy(curr->comm, comm, TASK_COMM_LEN);

        smp_mb(); /* Ensure that curr is initialized before insert */

        if (prev)
            prev->next = curr;
        else
            *head = curr;
    }
 out_unlock:
    raw_spin_unlock(&table_lock);

    return curr;
}

void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
                  void *timerf, char *comm,
                  unsigned int timer_flag)
{
    /*
     * It doesn't matter which lock we take:
     */
    raw_spinlock_t *lock;
    struct entry *entry, input;
    unsigned long flags;

    if (likely(!timer_stats_active))
        return;

    lock = &per_cpu(tstats_lookup_lock, raw_smp_processor_id());

    input.timer = timer;
    input.start_func = startf;
    input.expire_func = timerf;
    input.pid = pid;
    input.timer_flag = timer_flag;

    raw_spin_lock_irqsave(lock, flags);
    if (!timer_stats_active)
        goto out_unlock;

    entry = tstat_lookup(&input, comm);
    if (likely(entry))
        entry->count++;
    else
        atomic_inc(&overflow_count);

 out_unlock:
    raw_spin_unlock_irqrestore(lock, flags);
}

static void print_name_offset(struct seq_file *m, unsigned long addr)
{
    char symname[KSYM_NAME_LEN];

    if (lookup_symbol_name(addr, symname) < 0)
        seq_printf(m, "<%p>", (void *)addr);
    else
        seq_printf(m, "%s", symname);
}

static int tstats_show(struct seq_file *m, void *v)
{
    struct timespec period;
    struct entry *entry;
    unsigned long ms;
    long events = 0;
    ktime_t time;
    int i;

    mutex_lock(&show_mutex);
    /*
     * If still active then calculate up to now:
     */
    if (timer_stats_active)
        time_stop = ktime_get();

    time = ktime_sub(time_stop, time_start);

    period = ktime_to_timespec(time);
    ms = period.tv_nsec / 1000000;

    seq_puts(m, "Timer Stats Version: v0.2\n");
    seq_printf(m, "Sample period: %ld.%03ld s\n", period.tv_sec, ms);
    if (atomic_read(&overflow_count))
        seq_printf(m, "Overflow: %d entries\n",
            atomic_read(&overflow_count));

    for (i = 0; i < nr_entries; i++) {
        entry = entries + i;
        if (entry->timer_flag & TIMER_STATS_FLAG_DEFERRABLE) {
            seq_printf(m, "%4luD, %5d %-16s ",
                entry->count, entry->pid, entry->comm);
        } else {
            seq_printf(m, " %4lu, %5d %-16s ",
                entry->count, entry->pid, entry->comm);
        }

        print_name_offset(m, (unsigned long)entry->start_func);
        seq_puts(m, " (");
        print_name_offset(m, (unsigned long)entry->expire_func);
        seq_puts(m, ")\n");

        events += entry->count;
    }

    ms += period.tv_sec * 1000;
    if (!ms)
        ms = 1;

    if (events && period.tv_sec)
        seq_printf(m, "%ld total events, %ld.%03ld events/sec\n",
               events, events * 1000 / ms,
               (events * 1000000 / ms) % 1000);
    else
        seq_printf(m, "%ld total events\n", events);

    mutex_unlock(&show_mutex);

    return 0;
}

/*
 * After a state change, make sure all concurrent lookup/update
 * activities have stopped:
 */
static void sync_access(void)
{
    unsigned long flags;
    int cpu;

    for_each_online_cpu(cpu) {
        raw_spinlock_t *lock = &per_cpu(tstats_lookup_lock, cpu);

        raw_spin_lock_irqsave(lock, flags);
        /* nothing */
        raw_spin_unlock_irqrestore(lock, flags);
    }
}

static ssize_t tstats_write(struct file *file, const char __user *buf,
                size_t count, loff_t *offs)
{
    char ctl[2];

    if (count != 2 || *offs)
        return -EINVAL;

    if (copy_from_user(ctl, buf, count))
        return -EFAULT;

    mutex_lock(&show_mutex);
    switch (ctl[0]) {
    case '0':
        if (timer_stats_active) {
            timer_stats_active = 0;
            time_stop = ktime_get();
            sync_access();
        }
        break;
    case '1':
        if (!timer_stats_active) {
            reset_entries();
            time_start = ktime_get();
            smp_mb();
            timer_stats_active = 1;
        }
        break;
    default:
        count = -EINVAL;
    }
    mutex_unlock(&show_mutex);

    return count;
}

static int tstats_open(struct inode *inode, struct file *filp)
{
    return single_open(filp, tstats_show, NULL);
}

static const struct file_operations tstats_fops = {
    .open       = tstats_open,
    .read       = seq_read,
    .write      = tstats_write,
    .llseek     = seq_lseek,
    .release    = single_release,
};

void __init init_timer_stats(void)
{
    int cpu;

    for_each_possible_cpu(cpu)
        raw_spin_lock_init(&per_cpu(tstats_lookup_lock, cpu));
}

static int __init init_tstats_procfs(void)
{
    struct proc_dir_entry *pe;

    pe = proc_create("timer_stats", 0644, NULL, &tstats_fops);
    if (!pe)
        return -ENOMEM;
    return 0;
}
__initcall(init_tstats_procfs);