Subject: Re: [Update][PATCH v7 7/7] cpufreq: schedutil: New governor based on
 scheduler utilization data
To: "Rafael J. Wysocki" <rafael@kernel.org>
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Cc: Viresh Kumar <viresh.kumar@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Juri Lelli <juri.lelli@arm.com>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Ingo Molnar <mingo@kernel.org>
From: Steve Muckle <steve.muckle@linaro.org>
Message-ID: <56FC80E0.9020206@linaro.org>
Date: Wed, 30 Mar 2016 18:44:00 -0700
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On 03/30/2016 10:24 AM, Rafael J. Wysocki wrote:
> On Wed, Mar 30, 2016 at 7:05 PM, Steve Muckle <steve.muckle@linaro.org> wrote:
>> On 03/30/2016 04:31 AM, Rafael J. Wysocki wrote:
>>>>>>> +static int sugov_limits(struct cpufreq_policy *policy)
>>>>>>> +{
>>>>>>> +     struct sugov_policy *sg_policy = policy->governor_data;
>>>>>>> +
>>>>>>> +     if (!policy->fast_switch_enabled) {
>>>>>>> +             mutex_lock(&sg_policy->work_lock);
>>>>>>> +
>>>>>>> +             if (policy->max < policy->cur)
>>>>>>> +                     __cpufreq_driver_target(policy, policy->max,
>>>>>>> +                                             CPUFREQ_RELATION_H);
>>>>>>> +             else if (policy->min > policy->cur)
>>>>>>> +                     __cpufreq_driver_target(policy, policy->min,
>>>>>>> +                                             CPUFREQ_RELATION_L);
>>>>>>> +
>>>>>>> +             mutex_unlock(&sg_policy->work_lock);
>>>>>>> +     }
>>>>>>> +
>>>>>>> +     sg_policy->need_freq_update = true;
>>>>>
>>>>> I am wondering why we need to do this for !fast_switch_enabled case?
>>>
>>> That will cause the rate limit to be ignored in the utilization update
>>> handler which may be necessary if it is set to a relatively large
>>> value (like 1 s).
>>
>> But why is that necessary for !fast_switch_enabled? In that case the
>> frequency has been adjusted to satisfy the new limits here, so ignoring
>> the rate limit shouldn't be necessary. In other words why not
>>
>> } else {
>>         sg_policy->need_freq_update = true;
>> }
> 
> My thinking here was that the governor might decide to use something
> different from the limit enforced here, so it would be good to make it
> do so as soon as possible.  In particular in the
> non-frequency-invariant utilization case in which new frequency
> depends on the current one.
> 
> That said i'm not particularly opposed to making that change if that's
> preferred.

Ah ok fair enough. No strong opinion from me...

thanks,
Steve