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 ;-)
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>
diff --git a/kernel/time/timer_stats.c b/kernel/time/timer_stats.c
index fa3d380..3216937 100644
--- a/kernel/time/timer_stats.c
+++ b/kernel/time/timer_stats.c
@@ -236,10 +236,15 @@
/*
* 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;
