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Date: Fri, 27 Nov 2009 03:55:13 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: =?iso-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>
Cc: Anton Blanchard <anton@samba.org>, mingo@elte.hu,
       linux-kernel@vger.kernel.org, msb@google.com
Subject: Re: PATCH: softlockup: Fix hung_task_check_count sysctl
Message-ID: <20091127025512.GB5406@nowhere>
References: <20091127022820.GU32182@kryten> <2375c9f90911261846i18a828eft391420b13bb3fbb2@mail.gmail.com>
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On Fri, Nov 27, 2009 at 10:46:53AM +0800, Am?rico Wang wrote:
> On Fri, Nov 27, 2009 at 10:28 AM, Anton Blanchard <anton@samba.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@samba.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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