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    SubjectRe: [RFC PATCH v3 03/10] PM: Introduce an Energy Model management framework
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    On 06/06/2018 06:26 PM, Quentin Perret wrote:
    > On Wednesday 06 Jun 2018 at 16:29:50 (+0100), Quentin Perret wrote:
    >> On Wednesday 06 Jun 2018 at 17:20:00 (+0200), Juri Lelli wrote:
    >>>>> This brings me to another question. Let's say there are multiple users of
    >>>>> the Energy Model in the system. Shouldn't the units of frequency and power
    >>>>> not standardized, maybe Mhz and mW?
    >>>>> The task scheduler doesn't care since it is only interested in power diffs
    >>>>> but other user might do.
    >>>>
    >>>> So the good thing about specifying units is that we can probably assume
    >>>> ranges on the values. If the power is in mW, assuming that we're talking
    >>>> about a single CPU, it'll probably fit in 16 bits. 65W/core should be
    >>>> a reasonable upper-bound ?
    >>>> But there are also vendors who might not be happy with disclosing absolute
    >>>> values ... These are sometimes considered sensitive and only relative
    >>>> numbers are discussed publicly. Now, you can also argue that we already
    >>>> have units specified in IPA for ex, and that it doesn't really matter if
    >>>> a driver "lies" about the real value, as long as the ratios are correct.
    >>>> And I guess that anyone can do measurement on the hardware and get those
    >>>> values anyway. So specifying a unit (mW) for the power is probably a
    >>>> good idea.
    >>>
    >>> Mmm, I remember we fought quite a bit while getting capacity-dmpis-mhz
    >>> binding accepted, and one of the musts was that the values were going to
    >>> be normalized. So, normalized power values again maybe?
    >>
    >> Hmmm, that's a very good point ... There should be no problems on the
    >> scheduler side -- we're only interested in correct ratios. But I'm not
    >> sure on the thermal side ... I will double check that.
    >
    > So, IPA needs to compare the power of the CPUs with the power of other
    > things (e.g. GPUs). So we can't normalize the power of the CPUs without
    > normalizing in the same scale the power of the other devices. I see two
    > possibilities:
    >
    > 1) we don't normalize the CPU power values, we specify them in mW, and
    > we document (and maybe throw a warning if we see an issue at runtime)
    > the max range of values. The max expected power for a single core
    > could be 65K for ex (16bits). And based on that we can verify
    > overflow and precision issues in the algorithms, and we keep it easy
    > to compare the CPU power numbers with other devices.

    I would say we need 1). 32bit values with units and proper documentation
    of the possible ranges.

    [...]

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