linux-kernel - Re: Re: [PATCH 05/15] sched/fair: Implement an EEVDF like policy

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Message-ID: <20231011073317.GJ14330@noisy.programming.kicks-ass.net>
Date:   Wed, 11 Oct 2023 09:33:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Abel Wu <wuyun.abel@...edance.com>
Cc:     Benjamin Segall <bsegall@...gle.com>, mingo@...nel.org,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.de, bristot@...hat.com,
        corbet@....net, qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, pjt@...gle.com, pavel@....cz,
        qperret@...gle.com, tim.c.chen@...ux.intel.com, joshdon@...gle.com,
        timj@....org, kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org, efault@....de,
        tglx@...utronix.de
Subject: Re: Re: [PATCH 05/15] sched/fair: Implement an EEVDF like policy

On Wed, Oct 11, 2023 at 12:14:30PM +0800, Abel Wu wrote:

> With Benjamin's fix, the semantics of 'Earliest Eligible' preserved.

Yeah, my bad.

> But since all this is about latency rather than fairness, I wonder if

It is about both, fairness is absolutely important.

> there are cases worthy of breaking the 'eligible' rule.

See the discussion with Youssef, if we weaken the eligible rule you get
horrific interference because you end up placing new tasks around the
0-lag point.