Re: [PATCH 0/4] CPUFreq statistics retrieved by drivers

[Lukasz Luba]

On 8/4/20 11:38 AM, Viresh Kumar wrote:
> On 04-08-20, 11:29, Lukasz Luba wrote:
> > On 8/4/20 6:35 AM, Viresh Kumar wrote:
> > > IIUC, the only concern right now is to capture stats with fast switch ? Maybe we
> > > can do something else in that case and brainstorm a bit..
> >
> > Correct, the fast switch is the only concern right now and not tracked. We
> > could fill in that information with statistics data from firmware
> > with a cpufreq driver help.
> >
> > I could make the if from patch 1/4 covering narrowed case, when
> > fast switch is present, check for drivers stats.
> > Something like:
> > -----------8<------------------------------------------------------------
> > if (policy->fast_switch_enabled)
> > 	if (policy->has_driver_stats)
> > 		return cpufreq_stats_present_driver_data(policy, buf);
> > 	else
> > 		return 0;
> > -------------->8----------------------------------------------------------
>
> I don't think doing it with help of firmware is the right thing to do
> here then. For another platform we may not have a firmware which can
> help us, we need something in the opp core itself for that. Lemme see
> if I can do something about it.

OK, great, I will wait then with this patch series v2 which would change
into debugfs scmi only. Could you please add me on CC, I am very
interested in.

> > > Why is firmware the governor here ? Aren't you talking about the simple fast
> > > switch case only ?
> >
> > I used a term 'governor' for the firmware because it makes the final
> > set for the frequency. It (FW) should respect the frequency value
> > set using the fast switch. I don't know how other firmware (e.g. Intel)
> > treats this fast switch value or if they even expose FW stats, though.
>
> For Intel I think, Linux is one of the entities that vote for deciding
> the frequency of the CPUs and the firmware (after taking all such
> factors into account) chooses a frequency by its own, which must be >=
> the frequency requested by Linux.
>
> > You can read about this statistics region in [1] at:
> > 4.5.5 Performance domain statistics shared memory region
> >
> > > Over that, I think this cpufreq stats information isn't parsed by any tool right
> > > now and tweaking it a bit won't hurt anyone (like if we start capturing things a
> > > bit differently). So we may not want to worry about breaking userspace ABI here,
> > > if what we are looking to do is the right thing to do.
> >
> > So, there is some hope... IMHO it would be better to have this cpufreq
> > stats in normal location, rather then in scmi debugfs.
>
> I agree.
>
> > > I am not sure what notifications are we talking about here.
> >
> > There is a notification mechanism described in the SCMI spec [1] at
> > 4.5.4 Notifications.
> > We were referring to that mechanism.
>
> Ahh, I see. All I was thinking was about the cpufreq specific
> notifiers :)