Re: [PATCH v5 3/5] cpufreq: report whether cpufreq supports Frequency Invariance (FI)

From: Ionela Voinescu <ionela.voinescu@arm.com>
To: Sudeep Holla <sudeep.holla@arm.com>
Cc: rjw@rjwysocki.net, viresh.kumar@linaro.org,
	dietmar.eggemann@arm.com, catalin.marinas@arm.com,
	will@kernel.org, valentin.schneider@arm.com,
	linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 3/5] cpufreq: report whether cpufreq supports Frequency Invariance (FI)
Date: Thu, 3 Sep 2020 14:45:08 +0100	[thread overview]
Message-ID: <20200903134508.GB29370@arm.com> (raw)
In-Reply-To: <20200902132838.GF25462@bogus>

Hi Sudeep,

Thank you for your review here and for the other patches.

On Wednesday 02 Sep 2020 at 14:28:38 (+0100), Sudeep Holla wrote:
[..]
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 4d5fe777184a..570bf2ebe9d4 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -61,6 +61,12 @@ static struct cpufreq_driver *cpufreq_driver;
> >  static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
> >  static DEFINE_RWLOCK(cpufreq_driver_lock);
> >  
> > +static DEFINE_STATIC_KEY_FALSE(cpufreq_freq_invariance);
> > +bool cpufreq_supports_freq_invariance(void)
> > +{
> > +	return static_branch_likely(&cpufreq_freq_invariance);
> > +}
> > +
> >  /* Flag to suspend/resume CPUFreq governors */
> >  static bool cpufreq_suspended;
> >  
> > @@ -2720,6 +2726,15 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
> >  	cpufreq_driver = driver_data;
> >  	write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >  
> > +	/*
> > +	 * Mark support for the scheduler's frequency invariance engine for
> > +	 * drivers that implement target(), target_index() or fast_switch().
> > +	 */
> > +	if (!cpufreq_driver->setpolicy) {
> > +		static_branch_enable_cpuslocked(&cpufreq_freq_invariance);
> > +		pr_debug("supports frequency invariance");
> > +	}
> > +
> >  	if (driver_data->setpolicy)
> 
> [super nit] while I understand cpufreq_driver = driver_data, it looks odd
> if 2 consecutive statements refer it with different variables. Or am I
> confusing myself hugely.
> 

No, you are right. If you look at the rest of the register function,
after cpufreq_driver = driver_data, both driver_data and cpufreq_driver
are used. For me using cpufreq_driver seemed more natural as after being
assigned driver_data, it will continue to be used after registration.

If it's alright with you I won't make this change for now. It's possible
that a better solution is to change the other occurrences of either
cpufreq_driver or driver_data in a separate patch, to make things
consistent across the function.

Thank you,
Ionela.

> -- 
> Regards,
> Sudeep