linux-kernel - [tip:sched/core] sched: Drop the need_resched() loop from cond

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Date:	Sat, 18 Jul 2009 14:21:31 GMT
From:	tip-bot for Frederic Weisbecker <fweisbec@...il.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	fweisbec@...il.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:sched/core] sched: Drop the need_resched() loop from cond_resched()

Commit-ID:  e7aaaa6934636d7a6cadd9e2a05250fbb6a34f65
Gitweb:     http://git.kernel.org/tip/e7aaaa6934636d7a6cadd9e2a05250fbb6a34f65
Author:     Frederic Weisbecker <fweisbec@...il.com>
AuthorDate: Thu, 16 Jul 2009 15:44:29 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sat, 18 Jul 2009 15:51:38 +0200

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>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <1247725694-6082-1-git-send-email-fweisbec@...il.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 kernel/sched.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 03f7e3f..4c5ee84 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)
--
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