linux-kernel - Re: [PATCH 0/4] Fix dvfs_headroom escaping uclamp constraints

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Message-ID: <20230826191752.xus6c7ssuuc2rssu@airbuntu>
Date:   Sat, 26 Aug 2023 20:17:52 +0100
From:   Qais Yousef <qyousef@...alina.io>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Lukasz Luba <lukasz.luba@....com>
Subject: Re: [PATCH 0/4] Fix dvfs_headroom escaping uclamp constraints

On 08/21/23 12:34, Rafael J. Wysocki wrote:
> On Sun, Aug 20, 2023 at 11:08 PM Qais Yousef <qyousef@...alina.io> wrote:
> >
> > DVFS headroom, or map_util_perf(), is applied after uclamp restrictions are
> > applied in effective_cpu_util(). This will lead to two problems for uclamp:
> >
> >         1. If util < uclamp_min, we'll run faster than uclamp_min. For example
> >            util = 50, uclamp_min = 100. map_util_perf() = 125 instead of 100.
> >
> >         2. If util > uclamp_max, we'll run faster than uclamp_max. For example
> >            util = 900, uclamp_max = 800, map_util_perf() = 1000.
> >
> > First patch rename the function to apply_dvfs_headroom() to reflect what it
> > really does. It is not really mapping util, but provides some headroom for the
> > util to grow. Provide a documentation for the function too.
> >
> > Second patch is the actual fix.
> >
> > Third patch moves apply_dvfs_headroom() to sched.h as there are no longer
> > users outside the scheduler.
> >
> > Fourth patch is an RFC to redefine what the headroom means for RT, DL and IRQ
> > pressures.
> >
> > Thanks!
> 
> For the first 3 patches in the series
> 
> Acked-by: Rafael J. Wysocki <rafael@...nel.org>

Thanks for having a look!


Cheers

--
Qais Yousef