linux-kernel - Re: [Eas-dev] [PATCH V3 1/3] sched: cpufreq: Allow remote cpufreq callbacks

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Date:   Wed, 26 Jul 2017 14:00:10 -0700
From:   Saravana Kannan <skannan@...eaurora.org>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
        Rafael Wysocki <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        eas-dev@...ts.linaro.org, smuckle.linux@...il.com,
        Len Brown <lenb@...nel.org>
Subject: Re: [Eas-dev] [PATCH V3 1/3] sched: cpufreq: Allow remote cpufreq
 callbacks

On 07/21/2017 06:03 AM, Peter Zijlstra wrote:
> On Thu, Jul 13, 2017 at 12:14:37PM +0530, Viresh Kumar wrote:
>> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
>> index 47e24b5384b3..606b1a37a1af 100644
>> --- a/drivers/cpufreq/cpufreq_governor.c
>> +++ b/drivers/cpufreq/cpufreq_governor.c
>> @@ -275,6 +275,10 @@ static void dbs_update_util_handler(struct update_util_data *data, u64 time,
>>   	struct policy_dbs_info *policy_dbs = cdbs->policy_dbs;
>>   	u64 delta_ns, lst;
>>
>> +	/* Don't allow remote callbacks */
>> +	if (smp_processor_id() != data->cpu)
>> +		return;
>> +
>
> The alternative is using some of that policy_dbs->policy->*cpus crud I
> suppose, because:

No, the alternative is to pass it on to the CPU freq driver and let it 
decide what it wants to do. That's the whole point if having a CPU freq 
driver -- so that the generic code doesn't need to care about HW 
specific details. Which is the point I was making in an earlier email to 
Viresh's patch -- we shouldn't be doing any CPU check for the call backs 
at the scheduler or ever governor level.

That would simplify this whole thing by deleting a bunch of code. And 
having much simpler checks in those drivers that actually have to deal 
with their HW specific details.


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