linux-kernel - Re: [PATCH v5 07/15] sched/core: uclamp: add clamp group bucketing support

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Message-ID: <20181112000910.GC3038@worktop>
Date:   Mon, 12 Nov 2018 01:09:10 +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 07/15] sched/core: uclamp: add clamp group bucketing
 support

On Mon, Oct 29, 2018 at 06:33:02PM +0000, Patrick Bellasi wrote:
> The number of clamp groups configured at compile time defines the range
> of utilization clamp values tracked by each CPU clamp group.
> For example, with the default configuration:
>    CONFIG_UCLAMP_GROUPS_COUNT 5
> we will have 5 clamp groups tracking 20% utilization each. In this case,
> a task with util_min=25% will have group_id=1.

OK I suppose; but should we not do a wholesale s/group/bucket/ at this
point?

We should probably raise the minimum number of buckets from 1 though :-)

> +/*
> + * uclamp_group_value: get the "group value" for a given "clamp value"
> + * @value: the utiliation "clamp value" to translate
> + *
> + * The number of clamp group, which is defined at compile time, allows to
> + * track a finite number of different clamp values. Thus clamp values are
> + * grouped into bins each one representing a different "group value".
> + * This method returns the "group value" corresponding to the specified
> + * "clamp value".
> + */
> +static inline unsigned int uclamp_group_value(unsigned int clamp_value)
> +{
> +#define UCLAMP_GROUP_DELTA (SCHED_CAPACITY_SCALE / CONFIG_UCLAMP_GROUPS_COUNT)
> +#define UCLAMP_GROUP_UPPER (UCLAMP_GROUP_DELTA * CONFIG_UCLAMP_GROUPS_COUNT)
> +
> +	if (clamp_value >= UCLAMP_GROUP_UPPER)
> +		return SCHED_CAPACITY_SCALE;
> +
> +	return UCLAMP_GROUP_DELTA * (clamp_value / UCLAMP_GROUP_DELTA);
> +}

Can't we further simplify; I mean, at this point all we really need to
know is the rq's highest group_id that is in use. We don't need to
actually track the value anymore.