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Date:   Wed, 7 Nov 2018 15:42:52 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Patrick Bellasi <patrick.bellasi@arm.com>
Cc:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Paul Turner <pjt@google.com>,
        Quentin Perret <quentin.perret@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Todd Kjos <tkjos@google.com>,
        Joel Fernandes <joelaf@google.com>,
        Steve Muckle <smuckle@google.com>,
        Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH v5 03/15] sched/core: uclamp: map TASK's clamp values
 into CPU's clamp groups
Message-ID: <20181107144252.GG9761@hirez.programming.kicks-ass.net>
References: <20181029183311.29175-1-patrick.bellasi@arm.com>
 <20181029183311.29175-4-patrick.bellasi@arm.com>
 <20181107121908.GO9781@hirez.programming.kicks-ass.net>
 <20181107141949.GF14309@e110439-lin>
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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.