diff options
| author | Ingo Molnar <mingo@elte.hu> | 2007-06-01 00:47:16 -0700 |
|---|---|---|
| committer | Chris Wright <chrisw@sous-sol.org> | 2007-06-11 11:36:48 -0700 |
| commit | cf019da09936867c2eea7bc75cf1b1d07e5827d3 (patch) | |
| tree | 21c2ee704b71b66a30063c5f563439c32f228825 | |
| parent | 7434011f268211af4a1e4977f5a1eb2004b1a690 (diff) | |
[PATCH] timer stats: speedups
Make timer-stats have almost zero overhead when enabled in the config but
not used. (this way distros can enable it more easily)
Also update the documentation about overhead of timer_stats - it was
written for the first version which had a global lock and a linear list
walk based lookup ;-)
Andrew says:
And this. Not a bugfix, but trivial and obvious and apparently some
distros don't want to enable timer_stats because of the performance
issue, but powertop uses timer_stats.
Ingo replies:
seconded. I have tested this with and without CONFIG_TIMER_STATS, with
and without timer_stats collection activated.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
| -rw-r--r-- | Documentation/hrtimer/timer_stats.txt | 7 | ||||
| -rw-r--r-- | kernel/time/timer_stats.c | 7 | ||||
| -rw-r--r-- | lib/Kconfig.debug | 5 |
3 files changed, 14 insertions, 5 deletions
diff --git a/Documentation/hrtimer/timer_stats.txt b/Documentation/hrtimer/timer_stats.txt index 27f782e3593f..22b0814d0ad0 100644 --- a/Documentation/hrtimer/timer_stats.txt +++ b/Documentation/hrtimer/timer_stats.txt @@ -2,9 +2,10 @@ timer_stats - timer usage statistics ------------------------------------ timer_stats is a debugging facility to make the timer (ab)usage in a Linux -system visible to kernel and userspace developers. It is not intended for -production usage as it adds significant overhead to the (hr)timer code and the -(hr)timer data structures. +system visible to kernel and userspace developers. If enabled in the config +but not used it has almost zero runtime overhead, and a relatively small +data structure overhead. Even if collection is enabled runtime all the +locking is per-CPU and lookup is hashed. timer_stats should be used by kernel and userspace developers to verify that their code does not make unduly use of timers. This helps to avoid unnecessary diff --git a/kernel/time/timer_stats.c b/kernel/time/timer_stats.c index e2923eda2576..73ddbeb4af3a 100644 --- a/kernel/time/timer_stats.c +++ b/kernel/time/timer_stats.c @@ -236,10 +236,15 @@ void timer_stats_update_stats(void *timer, pid_t pid, void *startf, /* * It doesnt matter which lock we take: */ - spinlock_t *lock = &per_cpu(lookup_lock, raw_smp_processor_id()); + 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; diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 3f3e7403dcac..c93a50246ae8 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -143,7 +143,10 @@ config TIMER_STATS reprogrammed. The statistics can be read from /proc/timer_stats. The statistics collection is started by writing 1 to /proc/timer_stats, writing 0 stops it. This feature is useful to collect information - about timer usage patterns in kernel and userspace. + about timer usage patterns in kernel and userspace. This feature + is lightweight if enabled in the kernel config but not activated + (it defaults to deactivated on bootup and will only be activated + if some application like powertop activates it explicitly). config DEBUG_SLAB bool "Debug slab memory allocations" |