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

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Message-ID: <2375c9f90911261846i18a828eft391420b13bb3fbb2@mail.gmail.com>
Date:	Fri, 27 Nov 2009 10:46:53 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Anton Blanchard <anton@...ba.org>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, msb@...gle.com,
	fweisbec@...il.com
Subject: Re: PATCH: softlockup: Fix hung_task_check_count sysctl

On Fri, Nov 27, 2009 at 10:28 AM, Anton Blanchard <anton@...ba.org> 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>


Ack.

I would also suggest to make 'max_count' as unsigned long,
since sysctl_hung_task_check_count is.

Thanks.

> ---
>
> 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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