linux-kernel - Re: Re: [PATCH 01/15] sched/fair: Add avg

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Message-ID: <3156c8fe-5488-4044-8282-79495bf89f6d@bytedance.com>
Date:   Wed, 11 Oct 2023 16:30:26 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        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 01/15] sched/fair: Add avg_vruntime

On 10/11/23 3:30 PM, Peter Zijlstra Wrote:
> On Wed, Oct 11, 2023 at 12:15:28PM +0800, Abel Wu wrote:
>> On 5/31/23 7:58 PM, Peter Zijlstra wrote:
>>> +/*
>>> + * Compute virtual time from the per-task service numbers:
>>> + *
>>> + * Fair schedulers conserve lag:
>>> + *
>>> + *   \Sum lag_i = 0
>>> + *
>>> + * Where lag_i is given by:
>>> + *
>>> + *   lag_i = S - s_i = w_i * (V - v_i)
>>
>> Since the ideal service time S is task-specific, should this be:
>>
>> 	lag_i = S_i - s_i = w_i * (V - v_i)
> 
> It is not, S is the same for all tasks. Remember, the base form is a
> differential equation and all tasks progress at the same time at dt/w_i
> while S progresses at dt/W.

IIUC it's V progresses at dt/W and is same for all tasks, not S which is
measured in real time (V*w_i).