perf_events: Improve task_sched_in()

This patch is an optimization in perf_event_task_sched_in() to avoid
scheduling the events twice in a row.

Without it, the perf_disable()/perf_enable() pair is invoked twice,
thereby pinned events counts while scheduling flexible events and we go
throuh hw_perf_enable() twice.

By encapsulating, the whole sequence into perf_disable()/perf_enable() we
ensure, hw_perf_enable() is going to be invoked only once because of the
refcount protection.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1268288765-5326-1-git-send-email-eranian@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 52c69a34d697..3853d49c7d56 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1368,6 +1368,8 @@ void perf_event_task_sched_in(struct task_struct *task)
         if (cpuctx->task_ctx == ctx)
                 return;
 
+        perf_disable();
+
         /*
          * We want to keep the following priority order:
          * cpu pinned (that don't need to move), task pinned,
@@ -1380,6 +1382,8 @@ void perf_event_task_sched_in(struct task_struct *task)
         ctx_sched_in(ctx, cpuctx, EVENT_FLEXIBLE);
 
         cpuctx->task_ctx = ctx;
+
+        perf_enable();
 }
 
 #define MAX_INTERRUPTS (~0ULL)