linux-kernel - [tip:perf/core] perf: Optimize perf_event_task_sched

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Date:	Sat, 21 Nov 2009 13:42:37 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:perf/core] perf: Optimize perf_event_task_sched_out

Commit-ID:  02ffdbc866c8b1c8644601e9aa6155700eed4c91
Gitweb:     http://git.kernel.org/tip/02ffdbc866c8b1c8644601e9aa6155700eed4c91
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Fri, 20 Nov 2009 22:19:50 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sat, 21 Nov 2009 14:11:38 +0100

perf: Optimize perf_event_task_sched_out

Remove an update_context_time() call from the
perf_event_task_sched_out() path and into the branch its needed.

The call was both superfluous, because __perf_event_sched_out()
already does it, and wrong, because it was done without holding
ctx->lock.

Place it in perf_event_sync_stat(), which is the only place it
is needed and which does already hold ctx->lock.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul Mackerras <paulus@...ba.org>
LKML-Reference: <20091120212508.779516394@...llo.nl>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/perf_event.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 9a18ff2..65f4dab 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1120,6 +1120,8 @@ static void perf_event_sync_stat(struct perf_event_context *ctx,
 	if (!ctx->nr_stat)
 		return;
 
+	update_context_time(ctx);
+
 	event = list_first_entry(&ctx->event_list,
 				   struct perf_event, event_entry);
 
@@ -1163,8 +1165,6 @@ void perf_event_task_sched_out(struct task_struct *task,
 	if (likely(!ctx || !cpuctx->task_ctx))
 		return;
 
-	update_context_time(ctx);
-
 	rcu_read_lock();
 	parent = rcu_dereference(ctx->parent_ctx);
 	next_ctx = next->perf_event_ctxp;
--
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