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

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Date:	Mon, 11 Jul 2016 13:24:04 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
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 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.