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

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Message-ID: <20091127025512.GB5406@nowhere>
Date:	Fri, 27 Nov 2009 03:55:13 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Anton Blanchard <anton@...ba.org>, 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 10:46:53AM +0800, Américo Wang wrote:
> 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.


Also, the batch_count thing should be dropped I think.
This is a hardcoded, not overridable pause after 1024
threads checks to avoid latencies caused by rcu_read_lock.
But now we have PREEMPT_RCU so people can enable it if
they care about latency. We should remove it as it adds
unnecessary complexity.

I'm preparing a patch for that, on top of Anton patch.

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