linux-kernel - Re: [PATCH v2 2/2] cpufreq: schedutil: Optimize operations with single max CPU capacity

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Message-ID: <a6b22f53-da3a-559b-9244-425ba0d7f9c3@arm.com>
Date:   Thu, 8 Dec 2022 08:43:16 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        rafael@...nel.org, dietmar.eggemann@....com,
        vincent.guittot@...aro.org, saravanak@...gle.com,
        wusamuel@...gle.com, isaacmanjarres@...gle.com,
        kernel-team@...roid.com, juri.lelli@...hat.com,
        peterz@...radead.org, mingo@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de
Subject: Re: [PATCH v2 2/2] cpufreq: schedutil: Optimize operations with
 single max CPU capacity



On 12/8/22 04:09, Viresh Kumar wrote:
> On 07-12-22, 10:17, Lukasz Luba wrote:
>> The max CPU capacity is the same for all CPUs sharing frequency domain
>> and thus 'policy' object. There is a way to avoid heavy operations
>> in a loop for each CPU by leveraging this knowledge. Thus, simplify
>> the looping code in the sugov_next_freq_shared() and drop heavy
>> multiplications. Instead, use simple max() to get the highest utilization
>> from these CPUs. This is useful for platforms with many (4 or 6) little
>> CPUs.
>>
>> The max CPU capacity must be fetched every time we are called, due to
>> difficulties during the policy setup, where we are not able to get the
>> normalized CPU capacity at the right time.
>>
>> The stored value in sugov_policy::max is also than used in
>> sugov_iowait_apply() to calculate the right boost. Thus, that field is
>> useful to have in that sugov_policy struct.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
>>   kernel/sched/cpufreq_schedutil.c | 22 +++++++++++-----------
>>   1 file changed, 11 insertions(+), 11 deletions(-)
> 
> Looks okay to me.
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> 

Thank you Viresh!

As Rafael said, it will wait after 6.2-rc1 is out.

Regards,
Lukasz