[tip:perf/core] perf_events: Improve task_sched_in()

[tip-bot for eranian@xxxxxxxxxx]

Commit-ID:  9b33fa6ba0e2f90fdf407501db801c2511121564
Gitweb:     http://git.kernel.org/tip/9b33fa6ba0e2f90fdf407501db801c2511121564
Author:     eranian@xxxxxxxxxx <eranian@xxxxxxxxxx>
AuthorDate: Wed, 10 Mar 2010 22:26:05 -0800
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Thu, 11 Mar 2010 15:23:28 +0100

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <1268288765-5326-1-git-send-email-eranian@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/perf_event.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 52c69a3..3853d49 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)
--
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