linux-kernel - Re: [PATCH] sched: check pinned tasks before nohz balance, linux-4.2-rc5

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Message-ID: <20150805152953.GB25159@twins.programming.kicks-ass.net>
Date:	Wed, 5 Aug 2015 17:29:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Uladzislau Rezki <urezki@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Mike Galbraith <efault@....de>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched: check pinned tasks before nohz balance,
 linux-4.2-rc5

On Wed, Aug 05, 2015 at 05:14:34PM +0200, Uladzislau Rezki wrote:
> While investigating “load balancer” logic, I run into interesting
> behavior related
> to affinity and NO_HZ idle balance. Basically saying if there are two
> tasks running
> in certain rq and one of them is pinned/affined, then scheduler will
> trigger load
> balance on power collapsed core via soft irq.
> 
> The corner case here is it may fail to unbalance because of affinity, as a
> result core that has two tasks will interrupt any found idle one each its timer
> tick, what can lead to wasting of power, especially in mobile area, what is
> our case.
> 
> Do you have any concern with provided patch?

Yeah, I should go fix the set_cpus_allowed rework :/

lkml.kernel.org/r/20150515154333.712161952@...radead.org
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