linux-kernel - Re: [PATCH] sched/idle: Make idle poll dynamic per-cpu

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Message-ID: <3cd68923-660b-42d9-2fce-4cf5f9369d18@redhat.com>
Date:   Mon, 16 Jan 2023 11:06:50 +0100
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Daniel Bristot de Oliveira <bristot@...nel.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Joe Mario <jmario@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH] sched/idle: Make idle poll dynamic per-cpu

On 1/16/23 10:28, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@...nel.org> wrote:
> 
>>> Urgh, can we please make this a cpuidle governor thing or so? So that 
>>> we don't need to invent new interfaces and such.
>>
>> I think the desired property here would be to make this interface on top 
>> of pretty much any governor. Ie. have a governor, but also a way to drop 
>> any CPU into idle-poll, overriding that.
> 
> ... with the goal of having the best governor for power efficiency by 
> default - but also the ability to drop a handful of CPUs into the highest 
> performance / lowest latency idle mode.
> 
> It's a special kind of nested policy, for workload exceptions.

Yep, it is for the (extreme, but existing) case in which the user wants to skip idle driver
machinery (and overheads involved).

People use idle poll on high-frequency trading or to avoid scheduling out a vCPU,
but as the systems are becoming more dynamic (and shared), having this option dynamic
and per-cpu is useful...

-- Daniel
> Thanks,
> 
> 	Ingo
>