linux-kernel - Re: [PATCH 5/6] cpufreq: Support for fast frequency switching

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Date:	Thu, 3 Mar 2016 11:30:03 +0530
From:	Viresh Kumar <viresh.kumar@...aro.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>,
	Peter Zijlstra <peterz@...radead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH 5/6] cpufreq: Support for fast frequency switching

On 02-03-16, 03:12, Rafael J. Wysocki wrote:
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -1772,6 +1772,39 @@ EXPORT_SYMBOL(cpufreq_unregister_notifie
>   *                              GOVERNORS                            *
>   *********************************************************************/
>  
> +/**
> + * cpufreq_driver_fast_switch - Carry out a fast CPU frequency switch.
> + * @policy: cpufreq policy to switch the frequency for.
> + * @target_freq: New frequency to set (may be approximate).
> + * @relation: Relation to use for frequency selection.
> + *
> + * Carry out a fast frequency switch from interrupt context.
> + *
> + * This function must not be called if policy->fast_switch_possible is unset.
> + *
> + * Governors calling this function must guarantee that it will never be invoked
> + * twice in parallel for the same policy and that it will never be called in
> + * parallel with either ->target() or ->target_index() for the same policy.
> + *
> + * If CPUFREQ_ENTRY_INVALID is returned by the driver's ->fast_switch()
> + * callback, the hardware configuration must be preserved.
> + */
> +void cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
> +				unsigned int target_freq, unsigned int relation)
> +{
> +	unsigned int freq;
> +
> +	if (target_freq == policy->cur)

Maybe an unlikely() here ?

> +		return;
> +
> +	freq = cpufreq_driver->fast_switch(policy, target_freq, relation);
> +	if (freq != CPUFREQ_ENTRY_INVALID) {
> +		policy->cur = freq;

Hmm.. What will happen to the code relying on the cpufreq-notifiers
now ?

> +		trace_cpu_frequency(freq, smp_processor_id());
> +	}
> +}
> +EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch);

-- 
viresh