7420ae3bb9
Intel processors support additional software hint called EPB ("Energy
Performance Bias") to guide the hardware heuristic of power management
features to favor increasing dynamic performance or conserve energy
consumption.
Since this EPB hint is processor specific, the same value of hint can
result in different behavior across generations of processors.
commit 4ecc933b7d1f ("x86: intel_epb: Allow model specific normal EPB
value")' introduced capability to update the default power up EPB
based on the CPU model and updated the default EPB to 7 for Alder Lake
mobile CPUs.
The same change is required for other Alder Lake-N and Raptor Lake-P
mobile CPUs as the current default of 6 results in higher uncore power
consumption. This increase in power is related to memory clock
frequency setting based on the EPB value.
Depending on the EPB the minimum memory frequency is set by the
firmware. At EPB = 7, the minimum memory frequency is 1/4th compared to
EPB = 6. This results in significant power saving for idle and
semi-idle workload on a Chrome platform.
For example Change in power and performance from EPB change from 6 to 7
on Alder Lake-N:
Workload Performance diff (%) power diff
----------------------------------------------------
VP9 FHD30 0 (FPS) -218 mw
Google meet 0 (FPS) -385 mw
This 200+ mw power saving is very significant for mobile platform for
battery life and thermal reasons.
But as the workload demands more memory bandwidth, the memory frequency
will be increased very fast. There is no power savings for such busy
workloads.
For example:
Workload Performance diff (%) from EPB 6 to 7
-------------------------------------------------------
Speedometer 2.0 -0.8
WebGL Aquarium 10K
Fish -0.5
Unity 3D 2018 0.2
WebXPRT3 -0.5
There are run to run variations for performance scores for
such busy workloads. So the difference is not significant.
Add a new define ENERGY_PERF_BIAS_NORMAL_POWERSAVE for EPB 7
and use it for Alder Lake-N and Raptor Lake-P mobile CPUs.
This modification is done originally by
Jeremy Compostella <jeremy.compostella@intel.com>.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/all/20221027220056.1534264-1-srinivas.pandruvada%40linux.intel.com
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.