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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-11-16 14:38:16 +0100
committerIngo Molnar <mingo@elte.hu>2011-12-06 08:33:52 +0100
commit0f5a2601284237e2ba089389fd75d67f77626cef (patch)
tree37eedc660f09a36cfbd6b2a2c28e8cd0d1dbe167 /include
parentd6c1c49de577fa292af2449817364b7d89b574d8 (diff)
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 <gleb@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/n/tip-515yhoatehd3gza7we9fapaa@git.kernel.org Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include')
-rw-r--r--include/linux/perf_event.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index b1f89122bf6..cb44c9e7566 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;