linux-kernel - Re: [PATCH v2 06/13] sched: Store maximum per-cpu capacity in root domain

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Message-ID: <20160711101832.GN30909@twins.programming.kicks-ass.net>
Date:	Mon, 11 Jul 2016 12:18:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	mingo@...hat.com, dietmar.eggemann@....com, yuyang.du@...el.com,
	vincent.guittot@...aro.org, mgalbraith@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/13] sched: Store maximum per-cpu capacity in root
 domain

On Wed, Jun 22, 2016 at 06:03:17PM +0100, Morten Rasmussen wrote:
> @@ -6905,11 +6906,19 @@ static int build_sched_domains(const struct cpumask *cpu_map,
>  	/* Attach the domains */
>  	rcu_read_lock();
>  	for_each_cpu(i, cpu_map) {
> +		rq = cpu_rq(i);
>  		sd = *per_cpu_ptr(d.sd, i);
>  		cpu_attach_domain(sd, d.rd, i);
> +
> +		if (rq->cpu_capacity_orig > rq->rd->max_cpu_capacity)
> +			rq->rd->max_cpu_capacity = rq->cpu_capacity_orig;
>  	}

Should you not set that _before_ cpu_attach_domain(), such that the
state is up-to-date when its published?

Also, since its lockless, should we not use {READ,WRITE}_ONCE() with it?

>  	rcu_read_unlock();
>  
> +	if (rq)
> +		pr_info("span: %*pbl (max cpu_capacity = %lu)\n",
> +			cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
> +

While a single statement, it is multi line, please add brackets.

>  	ret = 0;
>  error: