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

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Message-ID: <c2dc2ff0-b565-a2da-b3fa-2f50eb2b2e77@arm.com>
Date:   Tue, 6 Dec 2022 11:08:20 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.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] cpufreq: schedutil: Optimize operations with single max
 CPU capacity



On 12/6/22 11:00, Rafael J. Wysocki wrote:
> On Tue, Dec 6, 2022 at 11:30 AM Lukasz Luba <lukasz.luba@....com> wrote:
>>
>>
>>
>> On 12/6/22 10:16, Viresh Kumar wrote:
>>> On 06-12-22, 10:10, 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>
>>>
>>> Can you please divide this into two patches, one for just moving max
>>> and one for looping optimization ? Else we may end up reverting
>>> everything once again.
>>>
>>
>> OK, I can do that. Thanks for having a look!
> 
> Also, please note that this material is unlikely to go into 6.2, so
> I'd prefer going back to it after 6.2-rc1 is out.

Yes, I understand. Thanks Rafael!