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

Andreas Herrmann
2018-07-17T14:03:36Z

On Tue, Jul 17, 2018 at 12:21:36PM +0200, Andreas Herrmann wrote:
> On Tue, Jul 17, 2018 at 12:09:21PM +0200, Rafael J. Wysocki wrote:

---8<---

> > OK, the patch is below.
> >
> > First, I hope that if "Collaborative Power Control" is disabled, it will
> > simply hide the PCCH object and so intel_pstate will still not load then.
>
> PCCH is hidden in that case.
>
> > The main question basically is what the OS is expected to do if
> > "Dynamic Power Savings Mode" is set. If we are *expected* to use
> > the PCC interface then, intel_pstate may not work in that case, but
> > I suspect that the PCC interface allows extra energy to be saved
> > over what is possible without it.
>
> I'll test it and see what happens.

I've tested it on top of v4.18-rc5-36-g30b06abfb92b. intel_pstate now
loads instead of pcc-cpufreq and system looks stable.

When disabling "Collaborative Power Control" no cpufreq driver is loaded
(as expected).

Performance (with kernbench) is as expected (always better than any
brew of pcc-cpufreq + misc modifications to this driver + partial
rollback of commit 554c8aa8ecad).

If you like you can add either Tested-by or
Reviewed-by: Andreas Herrmann <aherrmann@suse.com>

I think this patch should be tagged for 4.17-stable.

Thanks,

Andreas

> > ---
> > drivers/cpufreq/intel_pstate.c | 17 ++++++++++++++++-
> > 1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > Index: linux-pm/drivers/cpufreq/intel_pstate.c
> > ===================================================================
> > --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> > +++ linux-pm/drivers/cpufreq/intel_pstate.c
> > @@ -2391,6 +2391,18 @@ static bool __init intel_pstate_no_acpi_
> > return true;
> > }
> >
> > +static bool __init intel_pstate_no_acpi_pcch(void)
> > +{
> > + acpi_status status;
> > + acpi_handle handle;
> > +
> > + status = acpi_get_handle(NULL, "\\_SB", &handle);
> > + if (ACPI_FAILURE(status))
> > + return true;
> > +
> > + return !acpi_has_method(handle, "PCCH");
> > +}
> > +
> > static bool __init intel_pstate_has_acpi_ppc(void)
> > {
> > int i;
> > @@ -2450,7 +2462,10 @@ static bool __init intel_pstate_platform
> >
> > switch (plat_info[idx].data) {
> > case PSS:
> > - return intel_pstate_no_acpi_pss();
> > + if (!intel_pstate_no_acpi_pss())
> > + return false;
> > +
> > + return intel_pstate_no_acpi_pcch();
> > case PPC:
> > return intel_pstate_has_acpi_ppc() && !force_load;
> > }
> >
> >