linux-kernel - Re: [PATCH 07/16] sched: Make SD_BALANCE

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Message-ID: <20160524235249.GH18670@intel.com>
Date:	Wed, 25 May 2016 07:52:49 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	peterz@...radead.org, mingo@...hat.com, dietmar.eggemann@....com,
	vincent.guittot@...aro.org, mgalbraith@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/16] sched: Make SD_BALANCE_WAKE a topology flag

On Mon, May 23, 2016 at 11:58:49AM +0100, Morten Rasmussen wrote:
> For systems with the SD_ASYM_CPUCAPACITY flag set on higher level in the
> sched_domain hierarchy we need a way to enable wake-up balancing for the
> lower levels as well as we may want to balance tasks that don't fit the
> capacity of the previous cpu.
> 
> We have the option of introducing a new topology flag to express this
> requirement, or let the existing SD_BALANCE_WAKE flag be set by the
> architecture as a topology flag. The former means introducing yet
> another flag, the latter breaks the current meaning of topology flags.
> None of the options are really desirable.
 
I'd propose to replace SD_WAKE_AFFINE with SD_BALANCE_WAKE. And the
SD_WAKE_AFFINE semantic is simply "waker allowed":

waker_allowed = cpumask_test_cpu(cpu, tsk_cpus_allowed(p));

This can be implemented without current functionality change.

>From there, the choice between waker and wakee, and fast path
select_idle_sibling() and the rest slow path should be reworked, which
I am thinking about.