linux-kernel - Re: [PATCHv4 11/12] sched/core: Disable SD_ASYM_CPUCAPACITY for root

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Message-ID: <20180720135410.GD19287@e105550-lin.cambridge.arm.com>
Date:   Fri, 20 Jul 2018 14:54:10 +0100
From:   Morten Rasmussen <morten.rasmussen@....com>
To:     Quentin Perret <quentin.perret@....com>
Cc:     peterz@...radead.org, mingo@...hat.com, valentin.schneider@....com,
        dietmar.eggemann@....com, vincent.guittot@...aro.org,
        gaku.inami.xh@...esas.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 11/12] sched/core: Disable SD_ASYM_CPUCAPACITY for
 root_domains without asymmetry

On Thu, Jul 05, 2018 at 04:03:11PM +0100, Quentin Perret wrote:
> On Thursday 05 Jul 2018 at 15:13:49 (+0100), Morten Rasmussen wrote:
> > 3. Detecting the flag in generic kernel/sched/* code means that all
> > architectures will pay the for the overhead when building/rebuilding the
> > sched_domain hierarchy, and all architectures that sets the cpu
> > capacities to asymmetric will set the flag whether they like it or not.
> > I'm not sure if this is a problem.
> 
> That is true as well ...
> 
> > 
> > In the end it is really about how much of this we want in generic code
> > and how much we hide in arch/, and if we dare to touch the sched_domain
> > build code ;-)
> 
> Right so you can argue that the arch code is here to give you a
> system-level information, and that if the scheduler wants to virtually
> split that system, then it's its job to make sure that happens properly.
> That is exactly what your patch does (IIUC), and I now think that this
> is a very sensible middle-ground option. But this is debatable so I'm
> interested to see what others think :-)

I went ahead an hacked up some patches that sets the flag automatically
as part of the sched_domain build process. I posted them so people can
have a look: 1532093554-30504-1-git-send-email-morten.rasmussen@....com

With those patches this patch has to be reverted/dropped.

Morten