Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 10 Apr 2018 08:55:14 +0200 | Subject | Re: [RFC PATCH 2/6] sched: Introduce energy models of CPUs |
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On Mon, Apr 9, 2018 at 6:42 PM, Quentin Perret <quentin.perret@arm.com> wrote: > On Monday 09 Apr 2018 at 17:32:33 (+0200), Peter Zijlstra wrote: >> On Mon, Apr 09, 2018 at 02:45:11PM +0100, Quentin Perret wrote: >> >> > In this specific patch, we are basically trying to figure out the >> > boundaries of frequency domains, and the power consumed by each CPU >> > at each OPP, to make them available to the scheduler. The important >> > thing here is that, in both cases, we rely on the OPP library to >> > keep the code as platform-agnostic as possible. >> >> AFAICT the only users of this PM_OPP stuff is a bunch of ARM platforms. > > That's correct. > >> Granted, body else has build a big.little style system, so that might >> all be fine I suppose. >> >> It won't be until some !ARM chip comes along that we'll know how >> generically usable any of this really is. >> > > Right. There is already a lot of diversity in the Arm ecosystem that has > to be managed. That's what I meant by platform-agnostic. Now, I agree > that it should be discussed whether or not this is enough for other > archs ...
Even for ARM64 w/ ACPI, mind you.
> It might be reasonable to expect from the archs who want to use EAS that > they expose their OPPs in the OPP lib. That should be harmless, and EAS > needs to know about the OPPs, so they should be made visible, ideally > somewhere generic. Otherwise, that means the interface with the > EAS has to be defined only by the energy model data structures, and the > actual energy model loading procedure becomes free-form arch code. > > I quiet like the first idea from a pure design standpoint, but I could > also understand if maintainers of other archs were reluctant to > have new dependencies on PM_OPP ...
Not just reluctant I would think.
Depending on PM_OPP directly here is like depending on ACPI directly. Would you agree with the latter?
>> > In the case of the frequency domains for example, the cpufreq driver is >> > in charge of specifying the CPUs that are sharing frequencies. That >> > information can come from DT, or SCPI, or SCMI, or whatever -- we >> > probably shouldn't have to care about that from the scheduler's >> > standpoint. That's why using dev_pm_opp_get_sharing_cpus() is handy, >> > the OPP library gives us the digested information we need. >> >> So I kinda would've expected to just ask cpufreq, that after all already >> knows these things. Why did we need to invent this pm_opp thing? > > Yes, we can definitely rely on cpufreq for this one. There is a "strong" > dependency on PM_OPP to get power values, so I decided to use PM_OPP for > the frequency domains as well, for consistency. But I can change that if > needed.
Yes, please.
>> >> Cpufreq has a tons of supported architectures, pm_opp not so much. >> >> > The power values (dev_pm_opp_get_power) we use right now are those >> > already used by the thermal subsystem (IPA), which means we don't have >> >> I love an IPA style beer, but I'm thinking that's not the same IPA, >> right :-) > > Well, both can help to chill down in a way ... :-) > > The IPA I'm talking about means Intelligent Power Allocator. It's a > thermal governor that uses a power model of the platform to allocate > power budgets to CPUs & GPUs using a control loop. The code is in > drivers/thermal/power_allocator.c if this is of interest. > >> >> > to introduce any new DT binding whatsoever. In a close future, the power >> > values could also come from other sources (SCMI for ex), and again it's >> > probably not the scheduler's job to care about those things, so the OPP >> > library is helping us again. As mentioned in the notes, as of today, this >> > approach has dependencies on other patches relating to these things which >> > are already on the list [1]. >> >> Is there any !ARM thermal driver? (clearly I'm not up-to-date on things >> thermal). > > I don't think so.
No, there isn't, AFAICS.
Thanks!
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