linux-kernel - Re: [RFC PATCH 04/19] cpufreq: bring data structures close to their locks

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Message-ID: <20160111220528.GJ6344@twins.programming.kicks-ass.net>
Date:	Mon, 11 Jan 2016 23:05:28 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Juri Lelli <juri.lelli@....com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	rjw@...ysocki.net, viresh.kumar@...aro.org,
	mturquette@...libre.com, steve.muckle@...aro.org,
	vincent.guittot@...aro.org, morten.rasmussen@....com,
	dietmar.eggemann@....com
Subject: Re: [RFC PATCH 04/19] cpufreq: bring data structures close to their
 locks

On Mon, Jan 11, 2016 at 05:35:45PM +0000, Juri Lelli wrote:
> +/**
> + * The "cpufreq driver" - the arch- or hardware-dependent low
> + * level driver of CPUFreq support, and its spinlock (cpufreq_driver_lock).
> + * This lock also protects cpufreq_cpu_data array and cpufreq_policy_list.
> + */
> +static struct cpufreq_driver *cpufreq_driver;
> +static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
>  static LIST_HEAD(cpufreq_policy_list);
> +static DEFINE_RWLOCK(cpufreq_driver_lock);

Part of my suggestion was to fold the per-cpu data of cpufreq_cpu_data
into struct cpufreq_driver.

That way each cpufreq_driver will have its own copy and there'd be only
the one global pointer to swizzle. Something very well suited to RCU.