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

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?

Thanks,
Rafael