Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 29 Mar 2023 09:50:51 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Josh Don <joshdon@google.com>
Cc:     mingo@kernel.org, vincent.guittot@linaro.org,
        linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, corbet@lwn.net,
        qyousef@layalina.io, chris.hyser@oracle.com,
        patrick.bellasi@matbug.net, pjt@google.com, pavel@ucw.cz,
        qperret@google.com, tim.c.chen@linux.intel.com, timj@gnu.org,
        kprateek.nayak@amd.com, yu.c.chen@intel.com,
        youssefesmat@chromium.org, joel@joelfernandes.org, efault@gmx.de
Subject: Re: [PATCH 04/17] sched/fair: Add avg_vruntime
Message-ID: <20230329075051.GJ4253@hirez.programming.kicks-ass.net>
References: <20230328092622.062917921@infradead.org>
 <20230328110353.853385546@infradead.org>
 <CABk29Nt-9MufWcyxr8=ghHDj_kUj21vkEw=4X10NpXncxN32uQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CABk29Nt-9MufWcyxr8=ghHDj_kUj21vkEw=4X10NpXncxN32uQ@mail.gmail.com>
Precedence: bulk

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@infradead.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.