linux-kernel - [tip:core/softlockup] softlockup: Fix hung_task_check

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Message-ID: <tip-e5af02261668350b43eb7381648930bde8e872f7@git.kernel.org>
Date:	Fri, 27 Nov 2009 05:48:47 GMT
From:	tip-bot for Anton Blanchard <anton@...ba.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, anton@...ba.org, hpa@...or.com,
	mingo@...hat.com, fweisbec@...il.com, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:core/softlockup] softlockup: Fix hung_task_check_count sysctl

Commit-ID:  e5af02261668350b43eb7381648930bde8e872f7
Gitweb:     http://git.kernel.org/tip/e5af02261668350b43eb7381648930bde8e872f7
Author:     Anton Blanchard <anton@...ba.org>
AuthorDate: Fri, 27 Nov 2009 13:28:20 +1100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 27 Nov 2009 06:21:57 +0100

softlockup: Fix hung_task_check_count sysctl

I'm seeing spikes of up to 0.5ms in khungtaskd on a large
machine. To reduce this source of jitter I tried setting
hung_task_check_count to 0:

 # echo 0 > /proc/sys/kernel/hung_task_check_count

which didn't have the intended response. Change to a post
increment of max_count, so a value of 0 means check 0 tasks.

Signed-off-by: Anton Blanchard <anton@...ba.org>
Acked-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: msb@...gle.com
LKML-Reference: <20091127022820.GU32182@...ten>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/hung_task.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index d4e8417..0c642d5 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -144,7 +144,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 
 	rcu_read_lock();
 	do_each_thread(g, t) {
-		if (!--max_count)
+		if (!max_count--)
 			goto unlock;
 		if (!--batch_count) {
 			batch_count = HUNG_TASK_BATCHING;
--
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