Messages in this thread | | | Date | Tue, 23 Jun 2009 17:08:03 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH/Resend] timer stats: add quick check to avoid function calls |
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* Heiko Carstens <heiko.carstens@de.ibm.com> wrote:
> 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
makes sense.
Only one very small detail:
> > 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;
Why is this declared twice, once in hrtimer.h and once in timer.h? One should suffice, right?
Ingo
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