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Srinivas Pandruvada 081690e941 powercap: intel_rapl: Fix invalid setting of Power Limit 4 
System runs at minimum performance, once powercap RAPL package domain
enabled flag is changed from 1 to 0 to 1.

Setting RAPL package domain enabled flag to 0, results in setting of
power limit 4 (PL4) MSR 0x601 to 0. This implies disabling PL4 limit.
The PL4 limit controls the peak power. So setting 0, results in some
undesirable performance, which depends on hardware implementation.

Even worse, when the enabled flag is set to 1 again. This will set PL4
MSR value to 0x01, which means reduce peak power to 0.125W. This will
force system to run at the lowest possible performance on every PL4
supported system.

Setting enabled flag should only affect the "enable" bit, not other
bits. Here it is changing power limit.

This is caused by a change which assumes that there is an enable bit in
the PL4 MSR like other power limits. Although PL4 enable/disable bit is
present with TPMI RAPL interface, it is not present with the MSR
interface.

There is a rapl_primitive_info defined for non existent PL4 enable bit
and then it is used with the commit 9050a9cd5e ("powercap: intel_rapl:
Cleanup Power Limits support") to enable PL4. This is wrong, hence remove
this rapl primitive for PL4. Also in the function
rapl_detect_powerlimit(), PL_ENABLE is used to check for the presence of
power limits. Replace PL_ENABLE with PL_LIMIT, as PL_LIMIT must be
present. Without this change, PL4 controls will not be available in the
sysfs once rapl primitive for PL4 is removed.

Fixes: 9050a9cd5e ("powercap: intel_rapl: Cleanup Power Limits support")
Suggested-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Tested-by: Sumeet Pawnikar <sumeet.r.pawnikar@intel.com>
Cc: 6.5+ <stable@vger.kernel.org> # 6.5+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2023-09-06 22:21:22 +02:00
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README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.