linux-kernel - Re: [PATCH v2 05/13] sched: Enable SD_BALANCE

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Message-ID: <20160712142612.GJ12540@e105550-lin.cambridge.arm.com>
Date:	Tue, 12 Jul 2016 15:26:13 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, dietmar.eggemann@....com, yuyang.du@...el.com,
	vincent.guittot@...aro.org, mgalbraith@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 05/13] sched: Enable SD_BALANCE_WAKE for asymmetric
 capacity systems

On Mon, Jul 11, 2016 at 01:24:04PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 11, 2016 at 12:04:58PM +0100, Morten Rasmussen wrote:
> 
> > One alternative to setting ASYM_CAP bottom up would be to set it only
> > where the asymmetry can be observed, and instead come up with a more
> > complicated way of setting BALANCE_WAKE bottom up until and including
> > the first level having the ASYM_CAP.
> 
> Right, that is what I was thinking.
> 
> > I looked at it briefly an realized that I couldn't find a clean way of
> > implementing it as I don't think we have visibility of which flags that
> > will be set at higher levels in the sched_domain hierarchy when the
> > lower levels are initialized. IOW, we have behavioural flags settings
> > depend on topology flags settings at a different level.
> 
> Looks doable if we pass @child into sd_init() in build_sched_domain().
> Then we could simply do:
> 
> 	*sd = (struct sched_domain){
> 		/* ... */
> 		.child = child,
> 	};
> 
> 	if (sd->flags & ASYM_CAP) {
> 		struct sched_domain *t = sd;
> 		while (t) {
> 			t->sd_flags |= BALANCE_WAKE;
> 			t = t->child;
> 		}
> 	}
> 
> Or something like that.

It appears to be working fine. I will roll it into v3 along with the
simpler and more sane ASYM_CAP semantics :)