linux-kernel - Re: [RFCv5 PATCH 01/46] arm: Frequency invariant scheduler load-tracking support

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Message-ID: <20150811092754.GS19282@twins.programming.kicks-ass.net>
Date:	Tue, 11 Aug 2015 11:27:54 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	mingo@...hat.com, vincent.guittot@...aro.org,
	daniel.lezcano@...aro.org,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	yuyang.du@...el.com, mturquette@...libre.com, rjw@...ysocki.net,
	Juri Lelli <Juri.Lelli@....com>, sgurrappadi@...dia.com,
	pang.xunlei@....com.cn, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, Russell King <linux@....linux.org.uk>
Subject: Re: [RFCv5 PATCH 01/46] arm: Frequency invariant scheduler
 load-tracking support

On Tue, Jul 07, 2015 at 07:23:44PM +0100, Morten Rasmussen wrote:
> +static DEFINE_PER_CPU(atomic_long_t, cpu_max_freq);
> +DEFINE_PER_CPU(atomic_long_t, cpu_freq_capacity);

> +	atomic_long_set(&per_cpu(cpu_freq_capacity, cpu), capacity);
> +	unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu));
> +		atomic_long_set(&per_cpu(cpu_max_freq, i), policy->max);
> +	unsigned long curr = atomic_long_read(&per_cpu(cpu_freq_capacity, cpu));

The use of atomic_long_t here is entirely pointless.

In fact (and someone needs to go fix this), its worse than
WRITE_ONCE()/READ_ONCE().
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