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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: Heiko 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: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Heiko Carstens 2009-06-23 17:38:15 +02:00 committed by Ingo Molnar
parent bfdb4d9f0f
commit 507e123151
4 changed files with 19 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/hrtimer.h
View File

@ -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));
}

4
include/linux/timer.h
View File

@ -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));
}

16
kernel/time/timer_stats.c
View File

@ -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:

2
kernel/timer.c
View File

@ -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;