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    SubjectRe: [PATCH v4 2/3] sched/fair: Take thermal pressure into account while estimating energy
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    On 6/16/21 6:24 PM, Dietmar Eggemann wrote:
    > On 15/06/2021 18:09, Lukasz Luba wrote:
    >>
    >> On 6/15/21 4:31 PM, Dietmar Eggemann wrote:
    >>> On 14/06/2021 21:11, Lukasz Luba wrote:
    >
    > [...]
    >
    >>> It's important to highlight that this will only fix this issue between
    >>> schedutil and EAS when it's due to `thermal pressure` (today only via
    >>> CPU cooling). There are other places which could restrict policy->max
    >>> via freq_qos_update_request() and EAS will be unaware of it.
    >>
    >> True, but for this I have some other plans.
    >
    > As long as people are aware of the fact that this was developed to be
    > beneficial for `EAS - IPA` integration, I'm fine with this.

    Good. I had in mind that I will have to do some re-work on this
    thermal pressure code in the cpufreq cooling, to satisfy our roadmap
    goals...

    >
    > [...]
    >
    >>> IMHO, this means that this is catered for the IPA governor then. I'm not
    >>> sure if this would be beneficial when another thermal governor is used?
    >>
    >> Yes, it will be, the cpufreq_set_cur_state() is called by
    >> thermal exported function:
    >> thermal_cdev_update()
    >>   __thermal_cdev_update()
    >>     thermal_cdev_set_cur_state()
    >>       cdev->ops->set_cur_state(cdev, target)
    >>
    >> So it can be called not only by IPA. All governors call it, because
    >> that's the default mechanism.
    >
    > True, but I'm still not convinced that it is useful outside `EAS - IPA`.

    It is. So in mainline thermal there is another governor: fair_share [1],
    which uses 'weights' to split the cooling effort across cooling devices
    in the thermal zone. That governor would manage CPUs and GPU and
    set throttling like IPA.

    >
    >>> The mechanical side of the code would allow for such benefits, I just
    >>> don't know if their CPU cooling device + thermal zone setups would cater
    >>> for this?
    >>
    >> Yes, it's possible. Even for custom vendor governors (modified clones
    >> of IPA)
    >
    > Let's stick to mainline here ;-) It's complicated enough ...

    I agree, so there isn't only IPA in mainline.

    >
    > [...]
    >
    >>> Maybe shorter?
    >>>
    >>>          struct cpumask *pd_mask = perf_domain_span(pd);
    >>> -       unsigned long cpu_cap =
    >>> arch_scale_cpu_capacity(cpumask_first(pd_mask));
    >>> +       int cpu = cpumask_first(pd_mask);
    >>> +       unsigned long cpu_cap = arch_scale_cpu_capacity(cpu);
    >>> +       unsigned long _cpu_cap = cpu_cap -
    >>> arch_scale_thermal_pressure(cpu);
    >>>          unsigned long max_util = 0, sum_util = 0;
    >>> -       unsigned long _cpu_cap = cpu_cap;
    >>> -       int cpu;
    >>> -
    >>> -       _cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
    >>
    >> Could be, but still, the definitions should be sorted from longest on
    >> top, to shortest at the bottom. I wanted to avoid modifying too many
    >> lines with this simple patch.
    >
    > Only if there are no dependencies, but here we have already `cpu_cap ->
    > pd_mask`. OK, not a big deal.

    True, those dependencies are tricky to sort them properly, so I coded
    it this way.

    [snip]

    >> I see what you mean, but this might cause some issues in the design
    >> (per-cpu scmi cpu perf control). Let's use this EM pointer gently ;)
    >
    > OK, with the requirement that clients see the EM as ro:
    >
    > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
    >

    Thank you Dietmar for the review!

    Regards,
    Lukasz

    [1]
    https://elixir.bootlin.com/linux/v5.13-rc6/source/drivers/thermal/gov_fair_share.c#L111

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