linux-kernel - Re: [PATCH v1 2/3] cpufreq: CPPC: Add per_cpu efficiency

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Date:   Thu, 17 Mar 2022 16:31:30 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Pierre Gondois <pierre.gondois@....com>
Cc:     linux-kernel@...r.kernel.org, Ionela.Voinescu@....com,
        Lukasz.Luba@....com, Morten.Rasmussen@....com,
        Dietmar.Eggemann@....com, mka@...omium.org,
        daniel.lezcano@...aro.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Fuad Tabba <tabba@...gle.com>, Rob Herring <robh@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v1 2/3] cpufreq: CPPC: Add per_cpu efficiency_class

On Thu, 17 Mar 2022 16:07:01 +0000,
Pierre Gondois <pierre.gondois@....com> wrote:
> 
> >> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> >> index 27df5c1e6baa..56637cbea5d6 100644
> >> --- a/arch/arm64/kernel/smp.c
> >> +++ b/arch/arm64/kernel/smp.c
> >> @@ -512,6 +512,7 @@ struct acpi_madt_generic_interrupt
> >> *acpi_cpu_get_madt_gicc(int cpu)
> >>   {
> >>   	return &cpu_madt_gicc[cpu];
> >>   }
> >> +EXPORT_SYMBOL(acpi_cpu_get_madt_gicc);
> > 
> > Why not EXPORT_SYMBOL_GPL()?
> 
> From what I understand, this could be made EXPORT_SYMBOL_GPL().
> The only reason was that the other symbol exportation in the
> file wasn't restricted to GPL.

I'm personally keen on keeping this for GPL code only, just like the
current code is. If there is a further need to relax this, we can
discuss it separately.

> 
> > 
> >> 
> >>   /*
> >>    * acpi_map_gic_cpu_interface - parse processor MADT entry
> >> diff --git a/drivers/cpufreq/cppc_cpufreq.c
> >> b/drivers/cpufreq/cppc_cpufreq.c
> >> index 8f950fe72765..a6cd95c3b474 100644
> >> --- a/drivers/cpufreq/cppc_cpufreq.c
> >> +++ b/drivers/cpufreq/cppc_cpufreq.c
> >> @@ -422,12 +422,66 @@ static unsigned int
> >> cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
> >>   	return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
> >>   }
> >> 
> >> +static bool efficiency_class_populated;
> >> +static DEFINE_PER_CPU(unsigned int, efficiency_class);
> >> +
> >> +static int populate_efficiency_class(void)
> >> +{
> >> +	unsigned int min = UINT_MAX, max = 0, class;
> >> +	struct acpi_madt_generic_interrupt *gicc;
> >> +	int cpu;
> >> +
> >> +	for_each_possible_cpu(cpu) {
> >> +		gicc = acpi_cpu_get_madt_gicc(cpu);
> >> +		if (!gicc)
> >> +			return -ENODEV;
> > 
> > How can that happen if you made it here using ACPI?
> 
> This is effectively an extra check. This could be removed.

Please do.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.