Messages in this thread | | | Date | Thu, 30 Jul 2020 10:10:14 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH 0/4] CPUFreq statistics retrieved by drivers |
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On Thu, Jul 30, 2020 at 02:23:33PM +0530, Viresh Kumar wrote: > On 29-07-20, 16:12, Lukasz Luba wrote: > > The existing CPUFreq framework does not tracks the statistics when the > > 'fast switch' is used or when firmware changes the frequency independently > > due to e.g. thermal reasons. However, the firmware might track the frequency > > changes and expose this to the kernel. > > > > This patch set aims to introduce CPUfreq statistics gathered by firmware > > and retrieved by CPUFreq driver. It would require a new API functions > > in the CPUFreq, which allows to poke drivers to get these stats. > > > > The needed CPUFreq infrastructure is in patch 1/4, patch 2/4 extends > > ARM SCMI protocol layer, patches 3/4, 4/4 modify ARM SCMI CPUFreq driver. > > Are you doing this for the fast switch case or because your platform > actually runs at frequencies which may be different from what cpufreq > core has requested ? >
I think so.
> I am also not sure what these tables should represent, what the > cpufreq core has decided for the CPUs or the frequencies we actually > run at, as these two can be very different for example if the hardware > runs at frequencies which don't match exactly to what is there in the > freq table. I believe these are rather to show what cpufreq and its > governors are doing with the CPUs. >
Exactly, I raised similar point in internal discussion and asked Lukasz to take up the same on the list. I assume it was always what cpufreq requested rather than what was delivered. So will we break the userspace ABI if we change that is the main question.
> Over that I would like the userspace stats to work exactly as the way > they work right now, i.e. capture all transitions from one freq to > other, not just time-in-state. Also resetting of the stats from > userspace for example. All allocation and printing of the data must be > done from stats core, the only thing which the driver would do at the > end is updating the stats structure and nothing more. Instead of > reading all stats from the firmware, it will be much easier if you can > just get the information from the firmware whenever there is a > frequency switch and then we can update the stats the way it is done > right now. And that would be simple. >
Good point, but notifications may not be lightweight. If that is no good, alternatively, I suggested to keep these firmware stats in a separate debugfs. Thoughts ?
-- Regards, Sudeep
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