linux-kernel - Re: [PATCH 1/7] sched/core: uclamp: add CPU clamp groups accounting

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Message-ID: <20180413084019.GQ4043@hirez.programming.kicks-ass.net>
Date:   Fri, 13 Apr 2018 10:40:19 +0200
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>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>
Subject: Re: [PATCH 1/7] sched/core: uclamp: add CPU clamp groups accounting

On Mon, Apr 09, 2018 at 05:56:09PM +0100, Patrick Bellasi wrote:
> +static inline void init_uclamp(void)

WTH is that inline?

> +{
> +	struct uclamp_cpu *uc_cpu;
> +	int clamp_id;
> +	int cpu;
> +
> +	mutex_init(&uclamp_mutex);
> +
> +	for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
> +		/* Init CPU's clamp groups */
> +		for_each_possible_cpu(cpu) {
> +			uc_cpu = &cpu_rq(cpu)->uclamp[clamp_id];
> +			memset(uc_cpu, UCLAMP_NONE, sizeof(struct uclamp_cpu));
> +		}
> +	}

Those loops are the wrong way around, this shreds your cache. This is a
slow path so it doesn't much matter, but it is sloppy.

> +}