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

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Date:	Wed, 29 Feb 2012 10:17:03 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Dan Williams <dan.j.williams@...el.com>
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 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.


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