linux-kernel - Re: [PATCH V2 9/9] cpufreq: scmi: Use .register

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Message-ID: <31d73514-0d60-3239-a727-0ae483f11c31@arm.com>
Date:   Wed, 11 Aug 2021 16:52:55 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Sudeep Holla <sudeep.holla@....com>,
        Cristian Marussi <cristian.marussi@....com>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 9/9] cpufreq: scmi: Use .register_em() callback



On 8/11/21 3:39 PM, Quentin Perret wrote:
> On Wednesday 11 Aug 2021 at 15:09:13 (+0100), Lukasz Luba wrote:
>>
>>
>> On 8/11/21 2:17 PM, Quentin Perret wrote:
>>> On Wednesday 11 Aug 2021 at 17:28:47 (+0530), Viresh Kumar wrote:
>>>> Set the newly added .register_em() callback to register with the EM
>>>> after the cpufreq policy is properly initialized.
>>>>
>>>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>>>> ---
>>>>    drivers/cpufreq/scmi-cpufreq.c | 55 ++++++++++++++++++++--------------
>>>>    1 file changed, 32 insertions(+), 23 deletions(-)
>>>>
>>>> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
>>>> index 75f818d04b48..b916c9e22921 100644
>>>> --- a/drivers/cpufreq/scmi-cpufreq.c
>>>> +++ b/drivers/cpufreq/scmi-cpufreq.c
>>>> @@ -22,7 +22,9 @@
>>>>    struct scmi_data {
>>>>    	int domain_id;
>>>> +	int nr_opp;
>>>>    	struct device *cpu_dev;
>>>> +	cpumask_var_t opp_shared_cpus;
>>>
>>> Can we use policy->related_cpus and friends directly in the callback
>>
>> Unfortunately not. This tricky setup code was introduced because we may
>> have a platform with per-CPU policy, so single bit set in
>> policy->related_cpus, but we want EAS to be still working on set
>> of CPUs. That's why we construct temporary cpumask and pass it to EM.
> 
> Aha, I see this now. Hmm, those platforms better have AMUs then,
> otherwise PELT signals will be wonky ...

That's the plan, to have the AMUs. We suggest that, but reality would
tell... ;)

> 
> I was going to suggest using dev_pm_opp_get_sharing_cpus() from the
> callback instead, but maybe that's overkill as we'd need to allocate a
> temporary cpumask and all. So n/m this patch should be fine as is.
>