From 0f5a2601284237e2ba089389fd75d67f77626cef Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 16 Nov 2011 14:38:16 +0100 Subject: perf: Avoid a useless pmu_disable() in the perf-tick Gleb writes: > Currently pmu is disabled and re-enabled on each timer interrupt even > when no rotation or frequency adjustment is needed. On Intel CPU this > results in two writes into PERF_GLOBAL_CTRL MSR per tick. On bare metal > it does not cause significant slowdown, but when running perf in a virtual > machine it leads to 20% slowdown on my machine. Cure this by keeping a perf_event_context::nr_freq counter that counts the number of active events that require frequency adjustments and use this in a similar fashion to the already existing nr_events != nr_active test in perf_rotate_context(). By being able to exclude both rotation and frequency adjustments a-priory for the common case we can avoid the otherwise superfluous PMU disable. Suggested-by: Gleb Natapov Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-515yhoatehd3gza7we9fapaa@git.kernel.org Signed-off-by: Ingo Molnar --- include/linux/perf_event.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index b1f89122bf6a..cb44c9e75660 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -890,6 +890,7 @@ struct perf_event_context { int nr_active; int is_active; int nr_stat; + int nr_freq; int rotate_disable; atomic_t refcount; struct task_struct *task; -- cgit v1.2.3