Re: [RFC PATCH v3 0/5] Introduce Cpufreq Active Stats

[Lukasz Luba]

On 4/26/22 04:11, Viresh Kumar wrote:
> On 06-04-22, 23:08, Lukasz Luba wrote:
> > Hi all,
> >
> > This is the 3rd version of patch set which tries to address issues which are
> > due to missing proper information about CPU performance in time.
> >
> > The issue description:
> > 1. "Cpufreq statistics cover the time when CPUs are in idle states, so they
> >     are not suitable for certain purposes, like thermal control." Rafael [2]
> > 2. Thermal governor Intelligent Power Allocation (IPA) has to estimate power,
> >     for the last period, e.g. 100ms, for each CPU in the Cluster, to grant new
> >     power and set max possible frequency. Currently in some cases it gets big
> >     error, when the frequency of CPU changed in the middle. It is due to the
> >     fact that IPA reads the current frequency for the CPU, not aware of all
> >     other frequencies which were actively (not in idle) used in the last 100ms.
> >
> > This code focuses on tracking the events of idle entry/exit for each CPU
> > and combine them with the frequency tracked statistics inside internal
> > statistics arrays (per-CPU). In the old cpufreq stats we have one shared
> > statistics array for the policy (all CPUs) and not take into account
> > periods when each CPU was in idle.
> >
> > Sometimes the IPA error between old estimation signal and reality is quite
> > big (>50%).
>
> It would have been useful to show how the stats hierarchy looks in userspace
> now.

I haven't modify your current cpufreq stats, they are still counting
total time (idle + running) for the given frequency. I think this is
still useful for some userspace tools. These new proposed stats don't
have such sysfs interface to read them. I don't know if userspace would
be interested in this information (the running only time). IIRC Android
uses bpf mechanisms to get this information to the userspace.