linux-kernel - Re: [PATCH 3/3] thermal: cpu_cooling: Migrate to using the EM framework

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Date:   Wed, 10 Apr 2019 09:57:04 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     edubezval@...il.com, rui.zhang@...el.com, javi.merino@...nel.org,
        amit.kachhap@...il.com, rjw@...ysocki.net, will.deacon@....com,
        catalin.marinas@....com, daniel.lezcano@...aro.org,
        dietmar.eggemann@....com, ionela.voinescu@....com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/3] thermal: cpu_cooling: Migrate to using the EM
 framework

On Wednesday 10 Apr 2019 at 11:14:49 (+0530), Viresh Kumar wrote:
> On 28-03-19, 10:13, Quentin Perret wrote:
> > +static unsigned int get_state_freq(struct cpufreq_cooling_device *cpufreq_cdev,
> > +			      unsigned long state)
> > +{
> > +	struct cpufreq_policy *policy;
> > +	unsigned long idx;
> > +
> > +	/* Use the Energy Model table if available */
> > +	if (cpufreq_cdev->em) {
> > +		idx = cpufreq_cdev->max_level - state;
> > +		return cpufreq_cdev->em->table[idx].frequency;
> > +	}
> > +
> > +	/* Otherwise, fallback on the CPUFreq table */
> > +	policy = cpufreq_cdev->policy;
> > +	if (policy->freq_table_sorted == CPUFREQ_TABLE_SORTED_ASCENDING)
> 
> It is not guaranteed that the frequency table is sorted in any order, isn't it ?

Hmm, indeed... I thought cpufreq_table_validate_and_sort() was actively
sorting the table but it seems I was wrong.

But I _think_ in practice the freq table actually happens to be sorted
for the upstream cpufreq drivers with the CPUFREQ_IS_COOLING_DEV flag
set. Most of them use dev_pm_opp_init_cpufreq_table() which guarantees
the table is sorted and qoriq-cpufreq explicitly sorts the table. But
I'm not sure about qcom-cpufreq-hw ...

So, if the above is true, perhaps I could simply add a check to mandate
that policy->freq_table_sorted != CPUFREQ_TABLE_SORTED_UNSORTED for
cpu_cooling ? That shouldn't harm the existing users.

Do you happen to know a board where the table is unsorted ? Is it a
common use-case ?

If yes, then I'll probably need to drop the dependency on cpufreq's
freq_table and use something else to convert indexes into frequencies
(PM_OPP ?). Unless we can force-sort the table in the cpufreq core, but
that might require lots of changes to lots of drivers too.

> 
> > +		idx = cpufreq_cdev->max_level - state;
> > +	else
> > +		idx = state;
> 
> -- 
> viresh

Thanks,
Quentin