linux-kernel - Re: [PATCH 04/17] sched/fair: Add avg

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Message-ID: <20230329075051.GJ4253@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Mar 2023 09:50:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Don <joshdon@...gle.com>
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, timj@....org,
        kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org, efault@....de
Subject: Re: [PATCH 04/17] sched/fair: Add avg_vruntime

On Tue, Mar 28, 2023 at 04:57:49PM -0700, Josh Don wrote:
> On Tue, Mar 28, 2023 at 4:06 AM Peter Zijlstra <peterz@...radead.org> wrote:
> [...]
> > +/*
> > + * Compute virtual time from the per-task service numbers:
> > + *
> > + * Fair schedulers conserve lag: \Sum lag_i = 0
> > + *
> > + * lag_i = S - s_i = w_i * (V - v_i)
> > + *
> > + * \Sum lag_i = 0 -> \Sum w_i * (V - v_i) = V * \Sum w_i - \Sum w_i * v_i = 0
> 
> Small note: I think it would be helpful to label these symbols
> somewhere :) Weight  and vruntime are fairly obvious, but I don't
> think 'S' and 'V' are as clear. Are these non-virtual ideal service
> time, and average vruntime, respectively?

Yep, they are. I'll see what I can do with the comments.