Re: [PATCH] Revert "cpufreq: intel_pstate: Enable PPC enforcement for servers"

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

On Fri, 2016-06-03 at 00:00 +0200, Rafael J. Wysocki wrote:
> On Wednesday, June 01, 2016 05:41:57 PM Srinivas Pandruvada wrote:
> > 
> > This change reverts
> > 'commit 2b3ec7650584 ("cpufreq: intel_pstate: Enable PPC
> > enforcement for
> > servers")'
> > 
> > Intel P State uses max P-State as the max turbo P-State. This max
> > P-State
> > can be limited by ACPI _PSS table entry 0. After
> > 'commit 9522a2ff9cde ("cpufreq: intel_pstate: Enforce _PPC
> > limits")''
> > the _PSS table entry[0] will be used to cap max performance for
> > enterprise and performance server by default.
> > 
> > Even though this is correct processing, but when the performance
> > results
> > are compared with the version before the above commit, then
> > obviously the
> > results will be worse, if the _PSS table entry 0 is not the max
> > turbo
> > P-State.
> > 
> > So to minimize impact on performance, this revert will disable the
> > default
> > enforcement of ACPI _PSS and ACPI _PPC. So this feature can only
> > only be
> > explicitly activated by kernel command line
> > intel_pstate=support_acpi_ppc
> > 
> > Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel
> > .com>
> Thanks for the revert, but I'm wondering if we can explore one more
> option.
> 
> Namely, if _PSS doesn't contain the turbo state, but we know the
> turbo range is
> there from the CPU, we can still use it and interpret _PPC for the
> max state as
> a permission to go into the turbo range.
> 
> What do you think?
Looks like a good idea. I will experiment. What is your deadline for
-rc2 fixes?
It will give me more time to experiment and test.

Thanks,
Srinivas

> 
> Thanks,
> Rafael
> 
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