linux-kernel - [PATCH 1/7] sched: Drop the need_resched() loop from cond

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Message-Id: <1247725694-6082-1-git-send-email-fweisbec@gmail.com>
Date:	Thu, 16 Jul 2009 02:28:08 -0400
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 1/7] sched: Drop the need_resched() loop from cond_resched()

The schedule() function is a loop that reschedules the current task
while the TIF_NEED_RESCHED flag is set:

void schedule(void)
{
need_resched:
	/* schedule code */
	if (need_resched())
		goto need_resched;
}

And cond_resched() repeat this loop:

do {
	add_preempt_count(PREEMPT_ACTIVE);
	schedule();
	sub_preempt_count(PREEMPT_ACTIVE);
} while(need_resched());

This loop is needless because schedule() already did the check and
nothing can set TIF_NEED_RESCHED between schedule() exit and the loop
check in need_resched().

Then remove this needless loop.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/sched.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 75d2c1d..264b163 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6618,11 +6618,9 @@ static void __cond_resched(void)
 	 * PREEMPT_ACTIVE, which could trigger a second
 	 * cond_resched() call.
 	 */
-	do {
-		add_preempt_count(PREEMPT_ACTIVE);
-		schedule();
-		sub_preempt_count(PREEMPT_ACTIVE);
-	} while (need_resched());
+	add_preempt_count(PREEMPT_ACTIVE);
+	schedule();
+	sub_preempt_count(PREEMPT_ACTIVE);
 }
 
 int __sched _cond_resched(void)
-- 
1.6.2.3

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