linux-kernel - Re: [PATCH v4 3/5] cpufreq: report whether cpufreq supports Frequency Invariance (FI)

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Date:   Mon, 31 Aug 2020 16:44:08 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ionela Voinescu <ionela.voinescu@....com>
Cc:     rjw@...ysocki.net, dietmar.eggemann@....com,
        catalin.marinas@....com, sudeep.holla@....com, will@...nel.org,
        valentin.schneider@....com, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/5] cpufreq: report whether cpufreq supports
 Frequency Invariance (FI)

On 28-08-20, 18:33, Ionela Voinescu wrote:
> Now that the update of the FI scale factor is done in cpufreq core for
> selected functions - target(), target_index() and fast_switch(),
> we can provide feedback to the task scheduler and architecture code
> on whether cpufreq supports FI.
> 
> For this purpose provide an external function to expose whether the
> cpufreq drivers support FI, by using a static key.
> 
> The logic behind the enablement of cpufreq-based invariance is as
> follows:
>  - cpufreq-based invariance is disabled by default
>  - cpufreq-based invariance is enabled if any of the callbacks
>    above is implemented while the unsupported setpolicy() is not
> 
> The cpufreq_supports_freq_invariance() function only returns whether
> cpufreq is instrumented with the arch_set_freq_scale() calls that
> result in support for frequency invariance. Due to the lack of knowledge
> on whether the implementation of arch_set_freq_scale() actually results
> in the setting of a scale factor based on cpufreq information, it is up
> to the architecture code to ensure the setting and provision of the
> scale factor to the scheduler.
> 
> Signed-off-by: Ionela Voinescu <ionela.voinescu@....com>
> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/cpufreq.c | 16 ++++++++++++++++
>  include/linux/cpufreq.h   |  5 +++++
>  2 files changed, 21 insertions(+)

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh