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Subject: Re: [RFC PATCH 0/7] Introduce thermal pressure
To:     Juri Lelli <juri.lelli@gmail.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
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Cc:     Quentin Perret <quentin.perret@arm.com>,
        Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Zhang Rui <rui.zhang@intel.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Amit Kachhap <amit.kachhap@gmail.com>,
        viresh kumar <viresh.kumar@linaro.org>,
        Javi Merino <javi.merino@kernel.org>,
        Eduardo Valentin <edubezval@gmail.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        "open list:THERMAL" <linux-pm@vger.kernel.org>,
        Ionela Voinescu <ionela.voinescu@arm.com>
From:   Thara Gopinath <thara.gopinath@linaro.org>
Message-ID: <5BBE3206.2010407@linaro.org>
Date:   Wed, 10 Oct 2018 13:08:22 -0400
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On 10/10/2018 09:34 AM, Juri Lelli wrote:
> On 10/10/18 15:08, Vincent Guittot wrote:
>> On Wed, 10 Oct 2018 at 14:50, Juri Lelli <juri.lelli@gmail.com> wrote:
>>>
>>> On 10/10/18 14:34, Vincent Guittot wrote:
>>>> Hi  Juri,
>>>>
>>>> On Wed, 10 Oct 2018 at 14:23, Juri Lelli <juri.lelli@gmail.com> wrote:
>>>>>
>>>>> On 10/10/18 14:04, Vincent Guittot wrote:
>>>>>
>>>>> [...]
>>>>>
>>>>>> The problem was the same with RT, the cfs utilization was lower than
>>>>>> reality because RT steals soem cycle to CFS
>>>>>> So schedutil was selecting a lower frequency when cfs was running
>>>>>> whereas the CPU was fully used.
>>>>>> The same can happen with thermal:
>>>>>> cap the max freq because of thermal
>>>>>> the utilization with decrease.
>>>>>> remove the cap
>>>>>> the utilization is still low and you will select a low OPP because you
>>>>>> don't take into account cycle stolen by thermal like with RT
>>>>>
>>>>> What if we scale frequency component considering the capped temporary
>>>>> max?
>>>>
>>>> Do you mean using a kind of scale_thermal_capacity in accumulate_sum
>>>> when computing utilization ?
>>>
>>> Yeah, something like that I guess. So that we account for temporary
>>> "fake" 1024..
>>
>> But the utilization will not be invariant anymore across the system
> 
> Mmm, I guess I might be wrong, but I was thinking we should be able to
> deal with this similarly to what we do with cpus with different max
> capacities. So, another factor?  Because then, how do we handle other
> ways in which max freq can be restricted (e.g. from userspace as Javi
> was also mentioning)?

IMHO, user-space restrictions should be handled separately. It should
probably reflect as an update of capacity_orig and rebuilding of
scheduler structures as such a restriction is meant to stay for a long
duration.

Regards
Thara
> 


-- 
Regards
Thara