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Subject[PATCH/Resend] timer stats: add quick check to avoid function calls
From: Heiko Carstens <heiko.carstens@de.ibm.com>

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>
---

include/linux/hrtimer.h | 6 ++++++
include/linux/timer.h | 4 ++++
kernel/time/timer_stats.c | 16 ++++++++--------
kernel/timer.c | 2 ++
4 files changed, 20 insertions(+), 8 deletions(-)

Index: linux-2.6/include/linux/hrtimer.h
===================================================================
--- linux-2.6.orig/include/linux/hrtimer.h
+++ linux-2.6/include/linux/hrtimer.h
@@ -438,12 +438,16 @@ extern void sysrq_timer_list_show(void);
*/
#ifdef CONFIG_TIMER_STATS

+extern int timer_stats_active;
+
extern void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
void *timerf, char *comm,
unsigned int timer_flag);

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);
}
@@ -453,6 +457,8 @@ extern void __timer_stats_hrtimer_set_st

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));
}

Index: linux-2.6/include/linux/timer.h
===================================================================
--- linux-2.6.orig/include/linux/timer.h
+++ linux-2.6/include/linux/timer.h
@@ -187,6 +187,8 @@ extern unsigned long get_next_timer_inte
*/
#ifdef CONFIG_TIMER_STATS

+extern int timer_stats_active;
+
#define TIMER_STATS_FLAG_DEFERRABLE 0x1

extern void init_timer_stats(void);
@@ -200,6 +202,8 @@ extern void __timer_stats_timer_set_star

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));
}

Index: linux-2.6/kernel/timer.c
===================================================================
--- linux-2.6.orig/kernel/timer.c
+++ linux-2.6/kernel/timer.c
@@ -378,6 +378,8 @@ static void timer_stats_account_timer(st
{
unsigned int flag = 0;

+ if (likely(!timer->start_site))
+ return;
if (unlikely(tbase_get_deferrable(timer->base)))
flag |= TIMER_STATS_FLAG_DEFERRABLE;

Index: linux-2.6/kernel/time/timer_stats.c
===================================================================
--- linux-2.6.orig/kernel/time/timer_stats.c
+++ linux-2.6/kernel/time/timer_stats.c
@@ -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 *time
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 *time
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 *
/*
* 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
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:

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