Re: Commit 554c8aa8ecad causing severe performance degression with pcc-cpufreq

Andreas Herrmann
2018-07-17T09:27:21Z

On Tue, Jul 17, 2018 at 11:23:25AM +0200, Rafael J. Wysocki wrote:
> On Tue, Jul 17, 2018 at 11:11 AM, Andreas Herrmann <aherrmann@suse.com> wrote:
> > On Tue, Jul 17, 2018 at 11:06:29AM +0200, Rafael J. Wysocki wrote:
> >> On Tue, Jul 17, 2018 at 10:50 AM, Andreas Herrmann <aherrmann@suse.com> wrote:
> >>
> >> [cut]
> >>
> >> >
> >> > On balance before this commit users could use pcc-cpufreq but had
> >> > already suboptimal performance (compared to say intel_pstate driver
> >> > which can be used changing BIOS options).
> >>
> >> BTW, I wonder why you need to change the BIOS options for intel_pstate to load.
> >
> > I think this is because of (in intel_pstate_init()):
> >
> > /*
> > * The Intel pstate driver will be ignored if the platform
> > * firmware has its own power management modes.
> > */
> > if (intel_pstate_platform_pwr_mgmt_exists())
> > return -ENODEV;
> >
>
> OK, because of the "Proliant" entry, right?
>
> So it looks like we have an issue there. We find the entry and we
> look for _PSS. It is not there, so we assume that the firmware is
> expected to control performance, which is not the case. It looks like
> we also should look for the presence of the PCC interface in there.
>
> I can provide a patch for that, will you be able to test it?

Yes, I can test it.

> >> It should be initialized before pcc-cpufreq (according to their
> >> respective initcall levels), so in theory intel_pstate should be used
> >> by default on the affected systems anyway.
> >
> >> What BIOS settings need to be changed for that?
> >
> > Already answered in other mail.
>
> Indeed.

Andreas