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Message-ID: <20190123192201.GK13777@hirez.programming.kicks-ass.net>
Date: Wed, 23 Jan 2019 20:22:01 +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 v6 10/16] sched/core: Add uclamp_util_with()
On Wed, Jan 23, 2019 at 02:51:06PM +0000, Patrick Bellasi wrote:
> On 23-Jan 14:33, Peter Zijlstra wrote:
> > On Tue, Jan 15, 2019 at 10:15:07AM +0000, Patrick Bellasi wrote:
> > > +static __always_inline
> > > +unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
> > > + struct task_struct *p)
> > > {
> > > unsigned int min_util = READ_ONCE(rq->uclamp[UCLAMP_MIN].value);
> > > unsigned int max_util = READ_ONCE(rq->uclamp[UCLAMP_MAX].value);
> > >
> > > + if (p) {
> > > + min_util = max(min_util, uclamp_effective_value(p, UCLAMP_MIN));
> > > + max_util = max(max_util, uclamp_effective_value(p, UCLAMP_MAX));
> > > + }
> > > +
> >
> > Like I think you mentioned earlier; this doesn't look right at all.
>
> What we wanna do here is to compute what _will_ be the clamp values of
> a CPU if we enqueue *p on it.
>
> The code above starts from the current CPU clamp value and mimics what
> uclamp will do in case we move the task there... which is always a max
> aggregation.
Ah, then I misunderstood the purpose of this function.
> > Should that not be something like:
> >
> > lo = READ_ONCE(rq->uclamp[UCLAMP_MIN].value);
> > hi = READ_ONCE(rq->uclamp[UCLAMP_MAX].value);
> >
> > min_util = clamp(uclamp_effective(p, UCLAMP_MIN), lo, hi);
> > max_util = clamp(uclamp_effective(p, UCLAMP_MAX), lo, hi);
>
> Here you end up with a restriction of the task clamp (effective)
> clamps values considering the CPU clamps... which is different.
>
> Why do you think we should do that?... perhaps I'm missing something.
I was left with the impression from patch 7 that we don't compose clamps
right and throught that was what this code was supposed to do.
I'll have another look at this patch.
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