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

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Date:	Wed, 29 Feb 2012 11:49:39 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Thomas Gleixner <tglx@...utronix.de>, 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>
Subject: Re: [RFC PATCH] kick ksoftirqd more often to please soft lockup detector

On Wed, Feb 29, 2012 at 1:17 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2012-02-28 at 14:16 -0800, Dan Williams wrote:
>> Looks like everyone is guilty:
>>
>> [  422.765336] softirq took longer than 1/4 tick: 3 NET_RX ffffffff813f0aa0
>> ...
>> [  423.971878] softirq took longer than 1/4 tick: 4 BLOCK ffffffff812519c8
>> [  423.985093] softirq took longer than 1/4 tick: 6 TASKLET ffffffff8103422e
>> [  423.993157] softirq took longer than 1/4 tick: 7 SCHED ffffffff8105e2e1
>> [  424.001018] softirq took longer than 1/4 tick: 9 RCU ffffffff810a0fed
>> [  424.008691] softirq loop took longer than 1/2 tick need_resched:
>
> /me kicks himself for not printing the actual duration.. :-)
>
>> As expected whenever that 1/2 tick message gets emitted the softirq
>> handler is almost running in a need_resched() context.
>
> Yeah.. that's quite expected.
>
>> So is it a good idea to get more aggressive about scheduling ksoftrrqd?
>
> Nah, moving away from softirq more like. I'll put moving the
> load-balancer into a kthread on the todo list. And it looks like
> everybody else should move to kthreads too.

I seem to recall this running into resistance (but maybe things have
changed in the last few years)?

https://lkml.org/lkml/2007/6/29/155
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