linux-kernel - Re: [PATCH v5 03/15] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups

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Message-ID: <20181107141949.GF14309@e110439-lin>
Date:   Wed, 7 Nov 2018 14:19:49 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...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 v5 03/15] sched/core: uclamp: map TASK's clamp values
 into CPU's clamp groups

On 07-Nov 13:19, Peter Zijlstra wrote:
> On Mon, Oct 29, 2018 at 06:32:57PM +0000, Patrick Bellasi wrote:
> > +struct uclamp_se {
> > +	unsigned int value		: SCHED_CAPACITY_SHIFT + 1;
> > +	unsigned int group_id		: order_base_2(UCLAMP_GROUPS);
> 
> Are you sure about ob2() ? seems weird we'll end up with 0 for
> UCLAMP_GROUPS==1.

So, we have:

   #define UCLAMP_GROUPS (CONFIG_UCLAMP_GROUPS_COUNT + 1)

because one clamp group is always reserved for defaults.
Thus, ob2(in) is always called with n>=2.

... should be safe no ?

However, will check better again on v6 for possible corner-cases...

> > +	unsigned int mapped		: 1;
> > +};

-- 
#include <best/regards.h>

Patrick Bellasi