linux-kernel - PATCH: softlockup: Fix hung_task_check

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Message-ID: <20091127022820.GU32182@kryten>
Date:	Fri, 27 Nov 2009 13:28:20 +1100
From:	Anton Blanchard <anton@...ba.org>
To:	mingo@...e.hu
Cc:	linux-kernel@...r.kernel.org, msb@...gle.com, fweisbec@...il.com
Subject: PATCH: 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>
---

Index: linux.trees.git/kernel/hung_task.c
===================================================================
--- linux.trees.git.orig/kernel/hung_task.c	2009-11-27 13:11:46.000000000 +1100
+++ linux.trees.git/kernel/hung_task.c	2009-11-27 13:11:57.000000000 +1100
@@ -144,7 +144,7 @@ static void check_hung_uninterruptible_t
 
 	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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