linux-kernel - RE: Usecases for the per-task latency-nice attribute

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Message-ID: <9e705d2d22d040f4a170839466b38f5b@AcuMS.aculab.com>
Date:   Thu, 19 Sep 2019 09:06:47 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Tim Chen' <tim.c.chen@...ux.intel.com>,
        Parth Shah <parth@...ux.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        "subhra mazumdar" <subhra.mazumdar@...cle.com>,
        Valentin Schneider <valentin.schneider@....com>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "morten.rasmussen@....com" <morten.rasmussen@....com>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "pjt@...gle.com" <pjt@...gle.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "quentin.perret@....com" <quentin.perret@....com>,
        "dhaval.giani@...cle.com" <dhaval.giani@...cle.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "tj@...nel.org" <tj@...nel.org>,
        "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        "qais.yousef@....com" <qais.yousef@....com>
Subject: RE: Usecases for the per-task latency-nice attribute

From: Tim Chen
> Sent: 18 September 2019 18:16
...
> Some users are running machine learning batch tasks with AVX512, and have observed
> that these tasks affect the tasks needing a fast response.  They have to
> rely on manual CPU affinity to separate these tasks.  With appropriate
> latency hint on task, the scheduler can be taught to separate them.

Will (or can) the scheduler pre-empt a low priority process that is spinning
in userspace in order to allow a high priority (or low latency) process run
on that cpu?

My suspicion is that the process switch can't happen until (at least) the
next hardware interrupt - and possibly only a timer tick into the scheduler.

	David

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