Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH v5 03/14] PM: Introduce an Energy Model management framework | Date | Fri, 10 Aug 2018 13:13:22 +0200 |
| |
On Friday, August 10, 2018 11:12:18 AM CEST Quentin Perret wrote: > On Friday 10 Aug 2018 at 10:41:56 (+0200), Rafael J. Wysocki wrote: > > On Friday, August 10, 2018 10:15:39 AM CEST Quentin Perret wrote:
[cut]
> Agreed. EAS and IPA don't care about the absolute real power values, all > they care about is relative correctness. But what I really want to avoid > is having IPA getting the power of the GPUs in mW, and the power of CPUs > in an abstract scale without unit. That _will_ create problems eventually > IMO, because the behaviour is undefined. Specifying a unit everywhere is > an easy way to enforce a consistent design across sub-systems, that's > all.
OK
> > > What I am currently proposing is to keep the unit (mW) in the EM > > > framework so that migrating IPA to using it can be done in a (relatively) > > > painless way. On a system where drivers don't know the exact wattage, > > > then they should just 'lie' to the EM framework, but it's their job to > > > lie coherently to all subsystems and keep things consistent, because all > > > subsystems have specified power in comparable units. > > > > Alternatively, there could be a translation layer between EM and IPA. > > Hmm, interesting... What do you have in mind exactly ? What would you > put in that layer ?
Something able to say how the numbers used by EM and IPA are related. :-)
Do you think that IPA and EM will always need to use the same set of data for the CPU?
> > From my experience, if you want people to come up with some numbers, > > they will just choose them to game the system this way or another > > unless those numbers can be measured directly or are clearly documented. > > > > And if that happens and then you want to make any significant changes, > > you'll need to deal with "regressions" occuring because someone chose > > the numbers to make the system behave in a specific way and your changes > > break that. > > > > As a rule, I rather avoid requesting unknown numbers from people. :-) > > > > > Another solution to solve this problem could be to extend the EM > > > framework introduced by this patch and make it manage the EM of any > > > device, not just CPUs. Then we could just specify that all power costs > > > must be in the same scale, regardless of the actual unit, and register > > > the EM of CPUs, GPUs, ... > > > However, I was hoping that this patch as-is was enough for a first step, > > > and that this extension of the framework could be done in a second step ? > > > Thoughts ? > > > > > > In any case, if we decide to keep the mW unit for now, I should at least > > > explain clearly why in the commit message. > > > > Right. > > > > Actually, the unit is as good as any other, but you need to bear in mind that > > the numbers provided may not be realistic. > > As long as they're all correct in a relative way, that's fine by me :-)
OK
Thanks, Rafael
| |