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

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Date:   Wed, 7 Nov 2018 15:42:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
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 Wed, Nov 07, 2018 at 02:19:49PM +0000, Patrick Bellasi wrote:
> 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 ?

+config UCLAMP_GROUPS_COUNT
+       int "Number of different utilization clamp values supported"
+       range 0 32
+       default 5

0+1 == 1

Increase the min range and you should be good I think.