linux-kernel - [tip:timers/urgent] nohz: Fix nohz ratelimit

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Date:	Thu, 17 Jun 2010 17:39:39 GMT
From:	tip-bot for Peter Zijlstra <peterz@...radead.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, bmb@...enacr.com, hpa@...or.com,
	mingo@...hat.com, torvalds@...ux-foundation.org,
	a.p.zijlstra@...llo.nl, efault@....de, peterz@...radead.org,
	jkosina@...e.cz, alan@...rguk.ukuu.org.uk, jefdriesen@...enet.be,
	hirofumi@...l.parknet.co.jp, gregkh@...e.de, tglx@...utronix.de,
	cw@...f.org
Subject: [tip:timers/urgent] nohz: Fix nohz ratelimit

Commit-ID:  3310d4d38fbc514e7b18bd3b1eea8effdd63b5aa
Gitweb:     http://git.kernel.org/tip/3310d4d38fbc514e7b18bd3b1eea8effdd63b5aa
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 17 Jun 2010 18:02:37 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 17 Jun 2010 19:37:29 +0200

nohz: Fix nohz ratelimit

Chris Wedgwood reports that 39c0cbe (sched: Rate-limit nohz) causes a
serial console regression, unresponsiveness, and indeed it does. The
reason is that the nohz code is skipped even when the tick was already
stopped before the nohz_ratelimit(cpu) condition changed.

Move the nohz_ratelimit() check to the other conditions which prevent
long idle sleeps.

Reported-by: Chris Wedgwood <cw@...f.org>
Tested-by: Brian Bloniarz <bmb@...enacr.com>
Signed-off-by: Mike Galbraith <efault@....de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Greg KH <gregkh@...e.de>
Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
Cc: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc: Jef Driesen <jefdriesen@...enet.be>
LKML-Reference: <1276790557.27822.516.camel@...ns>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/time/tick-sched.c |    5 +----
 1 files changed, 1 insertions(+), 4 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 1d7b9bc..783fbad 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -315,9 +315,6 @@ void tick_nohz_stop_sched_tick(int inidle)
 		goto end;
 	}
 
-	if (nohz_ratelimit(cpu))
-		goto end;
-
 	ts->idle_calls++;
 	/* Read jiffies and the time when jiffies were updated last */
 	do {
@@ -328,7 +325,7 @@ void tick_nohz_stop_sched_tick(int inidle)
 	} while (read_seqretry(&xtime_lock, seq));
 
 	if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
-	    arch_needs_cpu(cpu)) {
+	    arch_needs_cpu(cpu) || nohz_ratelimit(cpu)) {
 		next_jiffies = last_jiffies + 1;
 		delta_jiffies = 1;
 	} else {
--
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