linux-kernel - Re: [PATCH 1/7] sched: Add static_key for asymmetric cpu capacity optimizations

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Message-ID: <20180219114930.GA4589@e105550-lin.cambridge.arm.com>
Date:   Mon, 19 Feb 2018 11:49:30 +0000
From:   Morten Rasmussen <morten.rasmussen@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Morten Rasmussen <morten.rasmussen@...s.arm.com>, mingo@...hat.com,
        valentin.schneider@....com, dietmar.eggemann@....com,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] sched: Add static_key for asymmetric cpu capacity
 optimizations

On Fri, Feb 16, 2018 at 05:51:23PM +0100, Peter Zijlstra wrote:
> On Fri, Feb 16, 2018 at 03:41:01PM +0000, Morten Rasmussen wrote:
> > On Fri, Feb 16, 2018 at 02:47:04PM +0100, Peter Zijlstra wrote:
> > > ? possibly with:
> > > 
> > > 	else
> > > 		static_branch_disable(&sched_asym_cpucapacity);
> > > 
> > > if you want to play funny games :-)
> > 
> > I thought about that too. It could make certain hotplug scenarios even
> > more expensive. I think we want the sched_asym_cpucapacity code to behave
> > even if SD_ASYM_CPUCAPACITY isn't set anywhere, so the static key would
> > be permanently from the point we detect asymmetry and leave it set. This
> > would be in line with how the smt static key works.
> 
> Fair enough..

Yeah, we can always add the 'else' bit later if we find a good reason to
do so.