linux-kernel - [PATCH] timer stats: fix quick check optimization

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Message-ID: <20090709092426.GA4943@osiris.boeblingen.de.ibm.com>
Date:	Thu, 9 Jul 2009 11:24:26 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] timer stats: fix quick check optimization

From: Heiko Carstens <heiko.carstens@...ibm.com>

git commit 507e1231 "timer stats: Optimize by adding quick check to avoid
function calls" added one wrong check so that one unnecessary function call
isn't elimated.
time_stats_account_hrtimer() checks if timer->start_pid isn't initialized
in order to find out if timer_stats_update_stats() should be called.
However start_pid is initialized with -1 instead of 0, so that the function
call always happens.
Check timer->start_site like in timer_stats_account_timer() to fix this.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 include/linux/hrtimer.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/include/linux/hrtimer.h
===================================================================
--- linux-2.6.orig/include/linux/hrtimer.h
+++ linux-2.6/include/linux/hrtimer.h
@@ -448,7 +448,7 @@ extern void timer_stats_update_stats(voi
 
 static inline void timer_stats_account_hrtimer(struct hrtimer *timer)
 {
-	if (likely(!timer->start_pid))
+	if (likely(!timer->start_site))
 		return;
 	timer_stats_update_stats(timer, timer->start_pid, timer->start_site,
 				 timer->function, timer->start_comm, 0);
--
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