linux-kernel - Re: [RFC PATCH] kick ksoftirqd more often to please soft lockup detector

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Message-ID: <CABE8wwtv2YDCYkk5C5waZCkdG3+9pMbwsKvuce0q-Kj=pnduwg@mail.gmail.com>
Date:	Tue, 28 Feb 2012 08:48:38 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	linux-scsi@...r.kernel.org, Lukasz Dorau <lukasz.dorau@...el.com>,
	James Bottomley <JBottomley@...allels.com>,
	Andrzej Jakowski <andrzej.jakowski@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH] kick ksoftirqd more often to please soft lockup detector

On Tue, Feb 28, 2012 at 1:48 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>> BUG: soft lockup - CPU#3 stuck for 22s! [kworker/3:1:78]
>
> So you're stuck in softirq for 22s+, max_restart is 10, this gives that
> on average you spend 2.2s+ per softirq invocation, this is completely
> absolutely bonkers. Softirq handlers should never consume significant
> amount of cpu-time.

I'm not sure whether this was just one __do_softirq() invocation, or
multiple.  I'll see if I can instrument this, but the suspicion is
that max_restart can't help when softirq is constantly re-triggered.
I'll also add the below patch to see if any single invocation is
violating these expectations.

--
Dan
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