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

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Message-ID: <51CB1AE9.5090709@gmail.com>
Date:	Wed, 26 Jun 2013 10:46:33 -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 6/26/13 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.

>
> IIRC it did work at some point but bitrotted a bit since. The good news is that
> the deadline scheduler wants to use it and I'll probably have to fix it up
> then.

Hmmm.... meaning I should not be expecting anything in the next couple 
of months? Any gut opinions on how to approach the nested problem - at 
least a quick hack for me to see if this option has any impact on our 
problem? eg., a CPU variable noting we already have the runqueue lock 
and no need to grab it a second time.

David
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