linux-kernel - Re: [PATCH v11 2/5] sched/core: uclamp: Propagate parent clamps

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Message-ID: <20190715164200.GA30862@blackbody.suse.cz>
Date:   Mon, 15 Jul 2019 18:42:00 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        Alessio Balsini <balsini@...roid.com>
Subject: Re: [PATCH v11 2/5] sched/core: uclamp: Propagate parent clamps

On Mon, Jul 08, 2019 at 09:43:54AM +0100, Patrick Bellasi <patrick.bellasi@....com> wrote:
> Since it's possible for a cpu.uclamp.min value to be bigger than the
> cpu.uclamp.max value, ensure local consistency by restricting each
> "protection"
> (i.e. min utilization) with the corresponding "limit" (i.e. max
> utilization).
I think this constraint should be mentioned in the Documentation/....

> +static void cpu_util_update_eff(struct cgroup_subsys_state *css)
> +{
> +	struct cgroup_subsys_state *top_css = css;
> +	struct uclamp_se *uc_se = NULL;
> +	unsigned int eff[UCLAMP_CNT];
> +	unsigned int clamp_id;
> +	unsigned int clamps;
> +
> +	css_for_each_descendant_pre(css, top_css) {
> +		uc_se = css_tg(css)->parent
> +			? css_tg(css)->parent->uclamp : NULL;
> +
> +		for_each_clamp_id(clamp_id) {
> +			/* Assume effective clamps matches requested clamps */
> +			eff[clamp_id] = css_tg(css)->uclamp_req[clamp_id].value;
> +			/* Cap effective clamps with parent's effective clamps */
> +			if (uc_se &&
> +			    eff[clamp_id] > uc_se[clamp_id].value) {
> +				eff[clamp_id] = uc_se[clamp_id].value;
> +			}
> +		}
> +		/* Ensure protection is always capped by limit */
> +		eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);
> +
> +		/* Propagate most restrictive effective clamps */
> +		clamps = 0x0;
> +		uc_se = css_tg(css)->uclamp;
(Nitpick only, reassigning child where was parent before decreases
readibility. IMO)

> +		for_each_clamp_id(clamp_id) {
> +			if (eff[clamp_id] == uc_se[clamp_id].value)
> +				continue;
> +			uc_se[clamp_id].value = eff[clamp_id];
> +			uc_se[clamp_id].bucket_id = uclamp_bucket_id(eff[clamp_id]);
Shouldn't these writes be synchronized with writes from
__setscheduler_uclamp()?

>