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Commit 507e1231 authored by Heiko Carstens's avatar Heiko Carstens Committed by Ingo Molnar
Browse files

timer stats: Optimize by adding quick check to avoid function calls 



When the kernel is configured with CONFIG_TIMER_STATS but timer
stats are runtime disabled we still get calls to
__timer_stats_timer_set_start_info which initializes some
fields in the corresponding struct timer_list.

So add some quick checks in the the timer stats setup functions
to avoid function calls to __timer_stats_timer_set_start_info
when timer stats are disabled.

In an artificial workload that does nothing but playing ping
pong with a single tcp packet via loopback this decreases cpu
consumption by 1 - 1.5%.

This is part of a modified function trace output on SLES11:

 perl-2497  [00] 28630647177732388 [+  125]: sk_reset_timer <-tcp_v4_rcv
 perl-2497  [00] 28630647177732513 [+  125]: mod_timer <-sk_reset_timer
 perl-2497  [00] 28630647177732638 [+  125]: __timer_stats_timer_set_start_info <-mod_timer
 perl-2497  [00] 28630647177732763 [+  125]: __mod_timer <-mod_timer
 perl-2497  [00] 28630647177732888 [+  125]: __timer_stats_timer_set_start_info <-__mod_timer
 perl-2497  [00] 28630647177733013 [+   93]: lock_timer_base <-__mod_timer

Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Mustafa Mesanovic <mustafa.mesanovic@de.ibm.com>
Cc: Arjan van de Ven <arjan@infradead.org>
LKML-Reference: <20090623153811.GA4641@osiris.boeblingen.de.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent bfdb4d9f

include/linux/hrtimer.h

+5 −0
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ 
#include <linux/list.h>

#include <linux/wait.h>

#include <linux/percpu.h>

#include <linux/timer.h>





struct hrtimer_clock_base;
@@ -447,6 +448,8 @@ extern void timer_stats_update_stats(void *timer, pid_t pid, void *startf, 


static inline void timer_stats_account_hrtimer(struct hrtimer *timer)

{

	if (likely(!timer->start_pid))

		return;

	timer_stats_update_stats(timer, timer->start_pid, timer->start_site,

				 timer->function, timer->start_comm, 0);

}
@@ -456,6 +459,8 @@ extern void __timer_stats_hrtimer_set_start_info(struct hrtimer *timer, 


static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)

{

	if (likely(!timer_stats_active))

		return;

	__timer_stats_hrtimer_set_start_info(timer, __builtin_return_address(0));

}

include/linux/timer.h

+4 −0
Original line number Diff line number Diff line
@@ -190,6 +190,8 @@ extern unsigned long get_next_timer_interrupt(unsigned long now); 
 */

#ifdef CONFIG_TIMER_STATS



extern int timer_stats_active;



#define TIMER_STATS_FLAG_DEFERRABLE	0x1



extern void init_timer_stats(void);
@@ -203,6 +205,8 @@ extern void __timer_stats_timer_set_start_info(struct timer_list *timer, 


static inline void timer_stats_timer_set_start_info(struct timer_list *timer)

{

	if (likely(!timer_stats_active))

		return;

	__timer_stats_timer_set_start_info(timer, __builtin_return_address(0));

}

kernel/time/timer_stats.c

+8 −8
Original line number Diff line number Diff line
@@ -96,7 +96,7 @@ static DEFINE_MUTEX(show_mutex); 
/*

 * Collection status, active/inactive:

 */

static int __read_mostly active;

int __read_mostly timer_stats_active;



/*

 * Beginning/end timestamps of measurement:
@@ -242,7 +242,7 @@ void timer_stats_update_stats(void *timer, pid_t pid, void *startf, 
	struct entry *entry, input;

	unsigned long flags;



	if (likely(!active))

	if (likely(!timer_stats_active))

		return;



	lock = &per_cpu(lookup_lock, raw_smp_processor_id());
@@ -254,7 +254,7 @@ void timer_stats_update_stats(void *timer, pid_t pid, void *startf, 
	input.timer_flag = timer_flag;



	spin_lock_irqsave(lock, flags);

	if (!active)

	if (!timer_stats_active)

		goto out_unlock;



	entry = tstat_lookup(&input, comm);
@@ -290,7 +290,7 @@ static int tstats_show(struct seq_file *m, void *v) 
	/*

	 * If still active then calculate up to now:

	 */

	if (active)

	if (timer_stats_active)

		time_stop = ktime_get();



	time = ktime_sub(time_stop, time_start);
@@ -368,18 +368,18 @@ static ssize_t tstats_write(struct file *file, const char __user *buf, 
	mutex_lock(&show_mutex);

	switch (ctl[0]) {

	case '0':

		if (active) {

			active = 0;

		if (timer_stats_active) {

			timer_stats_active = 0;

			time_stop = ktime_get();

			sync_access();

		}

		break;

	case '1':

		if (!active) {

		if (!timer_stats_active) {

			reset_entries();

			time_start = ktime_get();

			smp_mb();

			active = 1;

			timer_stats_active = 1;

		}

		break;

	default:

kernel/timer.c

+2 −0
Original line number Diff line number Diff line
@@ -380,6 +380,8 @@ static void timer_stats_account_timer(struct timer_list *timer) 
{

	unsigned int flag = 0;



	if (likely(!timer->start_site))

		return;

	if (unlikely(tbase_get_deferrable(timer->base)))

		flag |= TIMER_STATS_FLAG_DEFERRABLE;