Re: [PATCH v1] Revert "cpufreq: schedutil: Move max CPU capacity to sugov_policy"

[Lukasz Luba]

Hi Rafael and Sam

On 11/21/22 19:18, Rafael J. Wysocki wrote:
> On Fri, Nov 18, 2022 at 2:00 AM Sam Wu <wusamuel@xxxxxxxxxx> wrote:
> > On Wed, Nov 16, 2022 at 3:35 AM Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> > > Which mainline kernel version you use in pixel6?
> > I am using kernel version 6.1-rc5.
> > > Could you elaborate a bit how is it possible?
> > > Do you have the sg_policy setup properly (and at right time)?
> > > Do you have the cpu capacity from arch_scale_cpu_capacity()
> > > set correctly and at the right time during this cpufreq
> > > governor setup?
> > >
> > > IIRC in Android there is a different code for setting up the
> > > cpufreq sched governor clones. In mainline we don't have to do
> > > those tricks, so this might be the main difference.
> > This behavior is seen on the mainline kernel. There isn't any vendor code
> > modifying the behavior, and the schedutil governor is being used.
> > > Could you trace the value that is read from
> > > arch_scale_cpu_capacity() and share it with us?
> > > I suspect this value changes in time in your kernel.
> > There's an additional CPU capacity normalization step during
> > init_cpu_capacity_callback() that does not happen until all the CPUs come
> > online. However, the sugov_start() function can be called for a subset of
> > CPUs before all the CPUs are brought up and before the normalization of
> > the CPU capacity values, so there could be a stale value stored
> > in sugov_policy.max field.
>
> OK, the revert has been applied as 6.1-rc material, thanks!

I was on a business trip last week so couldn't check this.
Now I'm back and I've checked the booting sequence.
Yes, there is some race condition and the mechanism
using blocking_notifier_call_chain() in the cpufreq_online()
doesn't help while we are registering that schedutil
new policy.

I will have to go through those mechanisms and check them.
I agree, for now the best option is to revert the patch.

My apologies for introducing this issues.
Thanks Sam for capturing it.

Regards,
Lukasz