linux-kernel - Re: [PATCH V5 2/2] cpufreq: Process remote callbacks from any CPU if the platform permits

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Date:   Mon, 31 Jul 2017 14:20:18 -0700
From:   Saravana Kannan <skannan@...eaurora.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     Rafael Wysocki <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        smuckle.linux@...il.com, juri.lelli@....com,
        Morten.Rasmussen@....com, patrick.bellasi@....com,
        eas-dev@...ts.linaro.org, joelaf@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 2/2] cpufreq: Process remote callbacks from any CPU
 if the platform permits

On 07/27/2017 11:46 PM, Viresh Kumar wrote:
> On many platforms, CPUs can do DVFS across cpufreq policies. i.e CPU
> from policy-A can change frequency of CPUs belonging to policy-B.
>
> This is quite common in case of ARM platforms where we don't
> configure any per-cpu register.
>
> Add a flag to identify such platforms and update
> cpufreq_can_do_remote_dvfs() to allow remote callbacks if this flag is
> set.
>
> Also enable the flag for cpufreq-dt driver which is used only on ARM
> platforms currently.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>   drivers/cpufreq/cpufreq-dt.c |  1 +
>   include/linux/cpufreq.h      | 18 ++++++++++++++++--
>   2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
> index fef3c2160691..d83ab94d041a 100644
> --- a/drivers/cpufreq/cpufreq-dt.c
> +++ b/drivers/cpufreq/cpufreq-dt.c
> @@ -274,6 +274,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>   		transition_latency = CPUFREQ_ETERNAL;
>
>   	policy->cpuinfo.transition_latency = transition_latency;
> +	policy->dvfs_possible_from_any_cpu = true;
>
>   	return 0;
>
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index b3b6e8203e82..227cd0f13300 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -127,6 +127,15 @@ struct cpufreq_policy {
>   	 */
>   	unsigned int		transition_delay_us;
>
> +	/*
> +	 * Remote DVFS flag (Not added to the driver structure as we don't want
> +	 * to access another structure from scheduler hotpath).
> +	 *
> +	 * Should be set if CPUs can do DVFS on behalf of other CPUs from
> +	 * different cpufreq policies.
> +	 */
> +	bool			dvfs_possible_from_any_cpu;
> +

Seems reasonable. This is something that can be easily set by the driver.

>   	 /* Cached frequency lookup from cpufreq_driver_resolve_freq. */
>   	unsigned int cached_target_freq;
>   	int cached_resolved_idx;
> @@ -564,8 +573,13 @@ struct governor_attr {
>
>   static inline bool cpufreq_can_do_remote_dvfs(struct cpufreq_policy *policy)
>   {
> -	/* Allow remote callbacks only on the CPUs sharing cpufreq policy */
> -	if (cpumask_test_cpu(smp_processor_id(), policy->cpus))
> +	/*
> +	 * Allow remote callbacks if:
> +	 * - dvfs_possible_from_any_cpu flag is set
> +	 * - the local and remote CPUs share cpufreq policy
> +	 */
> +	if (policy->dvfs_possible_from_any_cpu ||
> +	    cpumask_test_cpu(smp_processor_id(), policy->cpus))
>   		return true;
>
>   	return false;
>

Acked-by: Saravana Kannan <skannan@...eaurora.org>


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