linux-kernel - Re: [RFC PATCH v3] sched/fair: select idle cpu from idle cpumask for task wakeup

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Message-ID: <jhjy2jexjs3.mognet@arm.com>
Date:   Fri, 06 Nov 2020 21:22:36 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     "Li\, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        tim.c.chen@...ux.intel.com, linux-kernel@...r.kernel.org,
        Aubrey Li <aubrey.li@...el.com>,
        Qais Yousef <qais.yousef@....com>,
        Jiang Biao <benbjiang@...il.com>
Subject: Re: [RFC PATCH v3] sched/fair: select idle cpu from idle cpumask for task wakeup


On 04/11/20 11:52, Li, Aubrey wrote:
> On 2020/11/4 3:27, Valentin Schneider wrote:
>>> +static DEFINE_PER_CPU(bool, cpu_idle_state);
>>
>> I would've expected this to be far less compact than a cpumask, but that's
>> not the story readelf is telling me. Objdump tells me this is recouping
>> some of the padding in .data..percpu, at least with the arm64 defconfig.
>>
>> In any case this ought to be better wrt cacheline bouncing, which I suppose
>> is what we ultimately want here.
>
> Yes, every CPU has a byte, so it may not be less than a cpumask. Probably I can
> put it into struct rq, do you have any better suggestions?
>

Not really, I'm afraid.