linux-kernel - Re: [PATCH v7 03/15] sched/core: uclamp: Add system default clamps

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Message-ID: <20190313195850.GT2482@worktop.programming.kicks-ass.net>
Date:   Wed, 13 Mar 2019 20:58:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-api@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v7 03/15] sched/core: uclamp: Add system default clamps

On Wed, Mar 13, 2019 at 05:09:40PM +0000, Patrick Bellasi wrote:
> On 13-Mar 15:32, Peter Zijlstra wrote:

> > I still think that this effective thing is backwards.

> With respect to the previous v6, I've now moved this concept to the
> patch where we actually use it for the first time.

> The "effective" values allows to efficiently enforce the most
> restrictive clamp value for a task at enqueue time by:
>  - not loosing track of the original request
>  - don't caring about updating non runnable tasks

My point is that you already had an effective value; namely p->uclamp[],
since patch 1.

This patch then changes that into something else, instead of adding
p->uclamp_orig[], and concequently has to update all sites that
previously used p->uclamp[], which is a lot of pointless churn.