linux-kernel - Re: [PATCH v3 05/13] sched: Introduce SD_ASYM_CPUCAPACITY sched

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Message-ID: <20160817092345.GF3391@e105550-lin.cambridge.arm.com>
Date:	Wed, 17 Aug 2016 10:23:45 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Yuyang Du <yuyang.du@...el.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Mike Galbraith <mgalbraith@...e.de>, sgurrappadi@...dia.com,
	freedom.tan@...iatek.com, keita.kobayashi.ym@...esas.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 05/13] sched: Introduce SD_ASYM_CPUCAPACITY
 sched_domain topology flag

On Wed, Aug 17, 2016 at 04:42:36PM +0800, Wanpeng Li wrote:
> 2016-07-25 21:34 GMT+08:00 Morten Rasmussen <morten.rasmussen@....com>:
> > Add a topology flag to the sched_domain hierarchy indicating the lowest
> > domain level where the full range of cpu capacities is represented by
> > the domain members for asymmetric capacity topologies (e.g. ARM
> > big.LITTLE).
> >
> > The flag is intended to indicate that extra care should be taken when
> > placing tasks on cpus and this level spans all the different types of
> > cpus found in the system (no need to look further up the domain
> > hierarchy). This information is currently only available through
> > iterating through the capacities of all the cpus at parent levels in the
> > sched_domain hierarchy.
> >
> > SD 2      [  0      1      2      3]  SD_ASYM_CPUCAPACITY
> >
> > SD 1      [  0      1] [   2      3]  !SD_ASYM_CPUCAPACITY
> >
> > cpu:         0      1      2      3
> > capacity:  756    756   1024   1024
> >
> > If the topology in the example above is duplicated to create an eight
> > cpu example with third sched_domain level on top (SD 3), this level
> > should not have the flag set (!SD_ASYM_CPUCAPACITY) as its two group
> > would both have all cpu capacities represented within them.
> 
> I didn't find the place where set SD_ASYM_CPUCAPACITY to any SDs in
> this patchset, but you have testing result in cover letter, where I
> miss?

The flag is supposed to be set by arch-specific code. I included a few
patches in v1 and v2 that set the flag for arch/arm. However, since they
are hopefully soon to be superseded by patches from Juri I dropped them
from the v3 posting and provided a pointer to branch containing this patch
set, Juri's patches, and few additional glue patches instead that
enabled the flag when necessary for arch/arm and arch/arm64.

Sorry for the confusion.
Morten