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

On Fri, Jun 3, 2016 at 12:05 AM, Srinivas Pandruvada
[off-list ref] wrote:

On Fri, 2016-06-03 at 00:00 +0200, Rafael J. Wysocki wrote:

quoted

On Wednesday, June 01, 2016 05:41:57 PM Srinivas Pandruvada wrote:

quoted

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.

That need not be -rc2 as far as I'm concerned.  Reverts are the last
resort IMO, so please take your time.