linux-kernel - Re: [RFC][PATCH 1/2] ARM64: add cpu topology definition

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Message-ID: <CAKfTPtDBJUy6smFuACjQNVywQUiQs_iPMFs9T6uCwJOX5f7e8w@mail.gmail.com>
Date:	Mon, 29 Jul 2013 12:28:24 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
Cc:	Hanjun Guo <hanjun.guo@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	Al Stone <al.stone@...aro.org>,
	Patch Tracking <patches@...aro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	linaro-acpi <linaro-acpi@...ts.linaro.org>,
	Will Deacon <Will.Deacon@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	Naresh Bhat <naresh.bhat@...aro.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC][PATCH 1/2] ARM64: add cpu topology definition

On 29 July 2013 12:15, Sudeep KarkadaNagesha
<Sudeep.KarkadaNagesha@....com> wrote:
> On 29/07/13 10:46, Vincent Guittot wrote:
>> On 27 July 2013 12:42, Hanjun Guo <hanjun.guo@...aro.org> wrote:
>>> Power aware scheduling needs the cpu topology information to improve the
>>> cpu scheduler decision making.
>>
>> It's not only power aware scheduling. The scheduler already uses
>> topology and cache sharing when  CONFIG_SCHED_MC and/or
>> CONFIG_SCHED_SMT are enable. So you should also add these configs for
>> arm64 so the scheduler can use it
>>
> Just for my knowledge, I thought power aware using SCHED_MC/SMT was
> removed. I see commit 8e7fbcbc22c12414bcc9dfdd683637f58fb32759 "sched:
> Remove stale power aware scheduling remnants and dysfunctional knobs"
> I may be missing something here.

It's a common mistake to mixed SCHED_MC and powersaving balance with
SCHED_MC. Only the powersaving policy has been removed but the
SCHED_MC and SCHED_SMT are always in the scheduler and gives perf
improvement on arm 32bits

>
> Regards,
> Sudeep
>
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