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

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  [PATCH] sched: check pinned tasks before nohz balance, linux-4.2-rc5 Uladzislau Rezki <urezki@gmail.com> - 2015-08-05 17:20 +0200
    Re: [PATCH] sched: check pinned tasks before nohz balance,  linux-4.2-rc5 Peter Zijlstra <peterz@infradead.org> - 2015-08-05 17:40 +0200

#1200866 — [PATCH] sched: check pinned tasks before nohz balance, linux-4.2-rc5

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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?

--
Uladzislau Rezki

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#1200913 — 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@infradead.org
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