linux-kernel - Re: PATCH: softlockup: Fix hung_task_check

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Message-ID: <20091127024054.GA5406@nowhere>
Date:	Fri, 27 Nov 2009 03:40:56 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Anton Blanchard <anton@...ba.org>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, msb@...gle.com
Subject: Re: PATCH: softlockup: Fix hung_task_check_count sysctl

On Fri, Nov 27, 2009 at 01:28:20PM +1100, Anton Blanchard wrote:
> 
> 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>


> ---
> 
> 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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