linux-kernel - Re: [RFC PATCH 1/2] sched: Clean up SD_BALANCE

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Message-ID: <20160531104121.GJ3190@twins.programming.kicks-ass.net>
Date:	Tue, 31 May 2016 12:41:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	umgwanakikbuti@...il.com, bsegall@...gle.com, pjt@...gle.com,
	morten.rasmussen@....com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com
Subject: Re: [RFC PATCH 1/2] sched: Clean up SD_BALANCE_WAKE flags in sched
 domain build-up

On Tue, May 31, 2016 at 09:31:32AM +0800, Yuyang Du wrote:
> On Tue, May 31, 2016 at 11:21:46AM +0200, Peter Zijlstra wrote:
> > On Tue, May 31, 2016 at 09:11:37AM +0800, Yuyang Du wrote:
> > > The SD_BALANCE_WAKE is irrelevant in the contexts of these two removals,
> > > and in addition SD_BALANCE_WAKE is not and should not be set in any
> > > sched_domain flags so far.
> > 
> > This Changelog doesn't make any sense...
> 
> How? SD_BALANCE_WAKE is not in any sched_domain flags (sd->flags), even if
> it is, it is not used anywhere, no?

It is and it is. See select_task_fair_rq():

	if (tmp->flags & sd_flags)

Now, as long as WAKE_AFFINE is also set, its hard to actually get into
the find_idlest_cpu() balancing, but if you clear all that you will
still get there.