linux-kernel - Re: [PATCH v4 2/2] cpufreq: add virtual-cpufreq driver

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Date:   Fri, 8 Dec 2023 10:18:51 +0900
From:   David Dai <davidai@...gle.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Saravana Kannan <saravanak@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Masami Hiramatsu <mhiramat@...gle.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Pavan Kondeti <quic_pkondeti@...cinc.com>,
        Gupta Pankaj <pankaj.gupta@....com>,
        Mel Gorman <mgorman@...e.de>, kernel-team@...roid.com,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] cpufreq: add virtual-cpufreq driver

Hi Viresh,

Apologies for the late reply,

On Wed, Nov 15, 2023 at 3:29 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 10-11-23, 17:49, David Dai wrote:
> > diff --git a/drivers/cpufreq/virtual-cpufreq.c b/drivers/cpufreq/virtual-cpufreq.c
> > +static unsigned int virt_cpufreq_set_perf(struct cpufreq_policy *policy)
> > +{
> > +     writel_relaxed(policy->cached_target_freq,
>
> Drivers shouldn't be using the cached_target_freq directly. Use the target freq
> or index passed from cpufreq core.

We were trying to avoid rounding to frequency table entries to provide
more accurate frequency requests. However, we didn't find any
significant power or performance regressions using the frequencies
from the table, so I'll send another patch series using your
suggestion.

>
> > +static int virt_cpufreq_cpu_exit(struct cpufreq_policy *policy)
> > +{
> > +     topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_VIRT, policy->related_cpus);
> > +     kfree(policy->freq_table);
> > +     policy->freq_table = NULL;
>
> No need of doing this. Also the order of above two calls is wrong anyway.

Can you clarify this point a bit more? Are you suggesting to just
remove setting policy->freq_table to NULL and swap the ordering
freeing the freq_table vs clearing the topology source? I can
alternatively use dev_pm_opp_free_cpufreq_table to mirror the init.

Thanks,
David

>
> --
> viresh