linux-kernel - Re: [PATCH v4 6/7] cpufreq: Support for fast frequency switching

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Message-ID: <20160316153550.GA6344@twins.programming.kicks-ass.net>
Date:	Wed, 16 Mar 2016 16:35:50 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v4 6/7] cpufreq: Support for fast frequency switching

On Wed, Mar 16, 2016 at 03:52:28PM +0100, Rafael J. Wysocki wrote:
> +/**
> + * cpufreq_enable_fast_switch - Enable fast frequency switching for policy.
> + * @policy: cpufreq policy to enable fast frequency switching for.
> + *
> + * Try to enable fast frequency switching for @policy.
> + *
> + * The attempt will fail if there is at least one transition notifier registered
> + * at this point, as fast frequency switching is quite fundamentally at odds
> + * with transition notifiers.  Thus if successful, it will make registration of
> + * transition notifiers fail going forward.
> + *
> + * Call under policy->rwsem.

Nobody reads a comment..

> + */
> +void cpufreq_enable_fast_switch(struct cpufreq_policy *policy)
> +{

	lockdep_assert_held(&policy->rwsem);

While everybody complains when there's a big nasty splat in their dmesg
;-)

> +	mutex_lock(&cpufreq_fast_switch_lock);
> +	if (policy->fast_switch_possible && cpufreq_fast_switch_count >= 0) {
> +		cpufreq_fast_switch_count++;
> +		policy->fast_switch_enabled = true;
> +	} else {
> +		pr_warn("cpufreq: CPU%u: Fast freqnency switching not enabled\n",
> +			policy->cpu);
> +	}
> +	mutex_unlock(&cpufreq_fast_switch_lock);
> +}