linux-kernel - Re: [RFCv3 PATCH 33/48] sched: Energy-aware wake-up task placement

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Date:	Tue, 24 Mar 2015 16:53:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	"yuyang.du@...el.com" <yuyang.du@...el.com>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"mturquette@...aro.org" <mturquette@...aro.org>,
	"nico@...aro.org" <nico@...aro.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFCv3 PATCH 33/48] sched: Energy-aware wake-up task placement

On Tue, Mar 24, 2015 at 03:42:42PM +0000, Morten Rasmussen wrote:
> Right, I agree that we should preferably do the normal thing for U ~= 1.
> We can restructure the wake-up path to follow that pattern, but we need
> to know U beforehand to choose the right path. U isn't just
> get_cpu_usage(prev_cpu) but some broader view of the of the cpu
> utilizations. For example, prev_cpu might be full, but everyone else is
> idle so we still want to try to do an energy aware wake-up on some other
> cpu. U could be the minium utilization of all cpus in prev_cpu's
> sd_llc, which is somewhat similar to what energy_aware_wake_cpu() does.

Yeah, or a setting in the root domain set by the regular periodic load
balancer; that already grew some mojo to determine this in a patch I
recently commented on.

> I guess energy_aware_wake_cpu() could be refactored to call
> select_idle_sibling() if it find U ~= 1?

Sure yeah, that's not the hard part I think.
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