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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 <tglx@timesys.com>

 *

 * 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 <d.pensator@gmail.com>

 *      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_SPINLOCK(table_lock);

/*

 * Per-CPU lookup locks for fast hash lookup:

 */

static DEFINE_PER_CPU(spinlock_t, lookup_lock);

/*

 * Mutex to serialize state changes with show-stats activities:

 */

static DEFINE_MUTEX(show_mutex);

/*

 * Collection status, active/inactive:

 */

static int __read_mostly 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;

        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:

        spin_unlock(&table_lock);

        return curr;

}

/**

 * timer_stats_update_stats - Update the statistics for a timer.

 * @timer:      pointer to either a timer_list or a hrtimer

 * @pid:        the pid of the task which set up the timer

 * @startf:     pointer to the function which did the timer setup

 * @timerf:     pointer to the timer callback function of the timer

 * @comm:       name of the process which set up the timer

 *

 * When the timer is already registered, then the event counter is

 * incremented. Otherwise the timer is registered in a free slot.

 */

void timer_stats_update_stats(void *timer, pid_t pid, void *startf,

                              void *timerf, char *comm,

                              unsigned int timer_flag)

{

        /*

         * It doesnt matter which lock we take:

         */

        spinlock_t *lock;

        struct entry *entry, input;

        unsigned long flags;

        if (likely(!active))

                return;

        lock = &per_cpu(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;

        spin_lock_irqsave(lock, flags);

        if (!active)

                goto out_unlock;

        entry = tstat_lookup(&input, comm);

        if (likely(entry))

                entry->count++;

        else

                atomic_inc(&overflow_count);

 out_unlock:

        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 (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) {

                spin_lock_irqsave(&per_cpu(lookup_lock, cpu), flags);

                /* nothing */

                spin_unlock_irqrestore(&per_cpu(lookup_lock, cpu), 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 (active) {

                        active = 0;

                        time_stop = ktime_get();

                        sync_access();

                }

                break;

        case '1':

                if (!active) {

                        reset_entries();

                        time_start = ktime_get();

                        smp_mb();

                        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 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)

                spin_lock_init(&per_cpu(lookup_lock, cpu));

}

static int __init init_tstats_procfs(void)

{

        struct proc_dir_entry *pe;

        pe = create_proc_entry("timer_stats", 0644, NULL);

        if (!pe)

                return -ENOMEM;

        pe->proc_fops = &tstats_fops;

        return 0;

}

__initcall(init_tstats_procfs);