linux-kernel - Re: [Update][PATCH v7 7/7] cpufreq: schedutil: New governor based on scheduler utilization data

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Date:	Fri, 1 Apr 2016 21:14:44 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [Update][PATCH v7 7/7] cpufreq: schedutil: New governor based on
 scheduler utilization data

On Fri, Apr 1, 2016 at 7:49 PM, Steve Muckle <steve.muckle@...aro.org> wrote:
> On 03/29/2016 07:00 PM, Rafael J. Wysocki wrote:
> ...
>> +config CPU_FREQ_GOV_SCHEDUTIL
>> +     tristate "'schedutil' cpufreq policy governor"
>> +     depends on CPU_FREQ
>> +     select CPU_FREQ_GOV_ATTR_SET
>> +     select IRQ_WORK
>> +     help
>> +       This governor makes decisions based on the utilization data provided
>> +       by the scheduler.  It sets the CPU frequency to be proportional to
>> +       the utilization/capacity ratio coming from the scheduler.  If the
>> +       utilization is frequency-invariant, the new frequency is also
>> +       proportional to the maximum available frequency.  If that is not the
>> +       case, it is proportional to the current frequency of the CPU with the
>> +       tipping point at utilization/capacity equal to 80%.
>
> This help text implies that the tipping point of 80% applies only to
> non-frequency invariant configurations, rather than both. Possible to
> rephrase?

Sure.

What about:

"If that is not the case, it is proportional to the current frequency
of the CPU.  The frequency tipping point is at utilization/capacity
equal to 80% in both cases."

> ...
>> +static unsigned int sugov_next_freq_shared(struct sugov_policy *sg_policy,
>> +                                        unsigned long util, unsigned long max)
>> +{
>> +     struct cpufreq_policy *policy = sg_policy->policy;
>> +     unsigned int max_f = policy->cpuinfo.max_freq;
>> +     u64 last_freq_update_time = sg_policy->last_freq_update_time;
>> +     unsigned int j;
>> +
>> +     if (util == ULONG_MAX)
>> +             return max_f;
>> +
>> +     for_each_cpu(j, policy->cpus) {
>> +             struct sugov_cpu *j_sg_cpu;
>> +             unsigned long j_util, j_max;
>> +             u64 delta_ns;
>> +
>> +             if (j == smp_processor_id())
>> +                     continue;
>> +
>> +             j_sg_cpu = &per_cpu(sugov_cpu, j);
>> +             /*
>> +              * If the CPU utilization was last updated before the previous
>> +              * frequency update and the time elapsed between the last update
>> +              * of the CPU utilization and the last frequency update is long
>> +              * enough, don't take the CPU into account as it probably is
>> +              * idle now.
>> +              */
>> +             delta_ns = last_freq_update_time - j_sg_cpu->last_update;
>> +             if ((s64)delta_ns > TICK_NSEC)
>
>>> Why not declare delta_ns as an s64 (also in suguv_should_update_freq)
>>> and avoid the cast?
>>
>> I took this from __update_load_avg(), but it shouldn't matter here.
>
> Did you mean to keep these casts?

Not really.  I'll fix that up shortly.