linux-kernel - Re: [PATCH V3 4/4] cpufreq: CPPC: Add support for frequency invariance

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Message-ID: <20210625085454.GA15540@arm.com>
Date:   Fri, 25 Jun 2021 09:54:54 +0100
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Sudeep Holla <sudeep.holla@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-pm@...r.kernel.org, Qian Cai <quic_qiancai@...cinc.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 4/4] cpufreq: CPPC: Add support for frequency
 invariance

Hey,

On Thursday 24 Jun 2021 at 18:34:18 (+0530), Viresh Kumar wrote:
> On 24-06-21, 10:48, Ionela Voinescu wrote:
> > On Monday 21 Jun 2021 at 14:49:37 (+0530), Viresh Kumar wrote:
> > > The Frequency Invariance Engine (FIE) is providing a frequency scaling
> > > correction factor that helps achieve more accurate load-tracking.
> > [..]
> > > +static void cppc_cpufreq_cpu_fie_exit(struct cpufreq_policy *policy)
> > > +{
> > > +	struct cppc_freq_invariance *cppc_fi;
> > > +	int cpu;
> > > +
> > > +	if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
> > > +		return;
> > > +
> > > +	/* policy->cpus will be empty here, use related_cpus instead */
> > > +	topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_CPPC, policy->related_cpus);
> > > +
> > > +	for_each_cpu(cpu, policy->related_cpus) {
> > > +		cppc_fi = &per_cpu(cppc_freq_inv, cpu);
> > 
> > Do you think it might be worth having here something like:
> > 
> > 		if (!cppc_fi->cpu_data)
> > 			continue;
> > 
> > This would be to protect against cases where the platform does not boot
> > with all CPUs or the module is loaded after some have already been
> > offlined. Unlikely, but..
> 
> Even in that case policy->cpus will contain all offline+online CPUs (at ->init()
> time), isn't it ?
> 

Right, my bad. I missed cpumask_and(policy->cpus, policy->cpus,
cpu_online_mask) being done after init(). It logically seems a bit
wrong, but drivers are in control of setting policy->cpus and acting on
it, and in this case the driver does the right thing.

Thanks,
Ionela.

> > > +		irq_work_sync(&cppc_fi->irq_work);
> > > +		kthread_cancel_work_sync(&cppc_fi->work);
> > > +	}
> > > +}
> > 
> > The rest of the code is almost the same as the original, so that is all
> > from me :).
> > 
> > Thanks,
> > Ionela.
> 
> -- 
> viresh