linux-kernel - Re: deadlock in scheduler enabling HRTICK feature

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Date:	Thu, 27 Jun 2013 16:28:57 -0600
From:	David Ahern <dsahern@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: deadlock in scheduler enabling HRTICK feature

On 6/27/13 4:43 AM, Peter Zijlstra wrote:
> On Wed, Jun 26, 2013 at 10:46:33AM -0600, David Ahern wrote:
>> On 6/26/13 1:05 AM, Peter Zijlstra wrote:
>>>> What is the expectation that the feature provides? not a whole lot of
>>>> documentation on it. I walked down the path wondering if it solved an odd
>>>> problem we are seeing with the CFS in 2.6.27 kernel.
>>>
>>> Its supposed to use hrtimers for slice expiry instead of the regular tick.
>>
>> So theoretically CPU bound tasks would get preempted sooner? That was my
>> guess/hope anyways.
>
> Doth the below worketh?

It doth.

Usually make -j 8 for a kernel build in a VM would lock it up pretty 
quickly. With the patch I was able to run full builds multiple times.

As for the solution you are avoiding the nesting by not waking up the 
softirq daemon.

I'll backport to 2.6.27 and see what happens. Thanks for the patch.

David

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