** Changed in: linux (Ubuntu Noble)
Importance: Undecided => Medium
--
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/2077470
Title:
[SRU][Noble] Bad EPP defaults cause performance regressions on select
Intel CPUs
Status in linux package in Ubuntu:
New
Status in linux source package in Noble:
In Progress
Bug description:
[ Impact ]
* Intel currently provides an Energy Performance Preference (EPP) tunable
via its intel_pstate
to control power management. It ranges from 0 (performance) to 255
(powersaving).
* When the governor is set to powersave, which is the default, the EPP value
of balance_performance
controls how the CPU frequency scaling occurs. However, on some platforms
(Emerald Rapids, Meteor
Lake, Arrow Lake) it is set to a very conservative value out of the box,
resulting in degraded
performance by default.
* These EPP tuning values work as a black-box and vary per-generation, so
having the latest values
available is important to keep systems running at maximum achievable
performance. Both Intel and
Canonical perform this kinds of tests and supply values.
[ Test Plan ]
* Perform a benchmark on a stock Ubuntu 24.04 image
* On Emerald Rapids:
* Change the EPP to 32 by executing
echo 32 | sudo tee
/sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference
* Observe the performance difference. In our internal testing, we found the
following results
when setting EPP to 32:
POV-Ray: 32% faster | 12% less energy
OpenSSL: 12% faster | energy within 1%
Build Linux Kernel: 29% faster | 18% less energy
* On Meteor Lake and Arrow Lake:
* Change the EPP to 64 by executing
echo 64 | sudo tee
/sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference
* Observe the performance difference. Intel found out the following for
Meteor Lake:
> Speedometer 2.1
> score: +19%
> Perf/watt: +5.25%
>
> Webxprt 4 score
> score: +12%
> Perf/watt: +6.12%
>
> 3DMark Wildlife extreme unlimited score
> score: +3.2%
> Perf/watt: +11.5%
>
> Geekbench6 MT
> score: +2.14%
> Perf/watt: +0.32%
>
> Also update balance_power EPP default to 179. With this change:
> Video Playback power is reduced by 52%
> Team video conference power is reduced by 35%
* The same outcome should be obtained from Arrow Lake as per Intel.
[ Where problems could occur ]
* The regression risks are very low. The CPU should perform in a more
efficient zone, resulting in
overall power savings, despite the more aggressive scaling. This was
verified using a Yokogawa WT310
power meter and an Emerald Rapids reference platform.
* Tests on Meteor Lake and Arrow Lake were performed by Intel. They were not
independently verified by
Canonical.
[ Other Info ]
* Patch for Emerald Rapids:
https://lore.kernel.org/lkml/Zqu6zjVMoiXwROBI@capivara/ (merged in 6.11-rc3
https://lore.kernel.org/lkml/cajz5v0hq3o7e3ygvfkbzjkjbx7pddyd9qc+re4efyzjs12o...@mail.gmail.com/)
* Patch for Meteor Lake:
https://lore.kernel.org/lkml/cajz5v0i8rnws9ogxxqvocg4rhhn7x3elcrupogrs1ip8hns...@mail.gmail.com/
* Patch for Arrow Lake:
https://lore.kernel.org/lkml/CAJZ5v0g+R6JK=T9EjmweRPKmcorw93JmPM4u-Z=pywv6kh7...@mail.gmail.com/
(both merged in 6.11-rc1
https://lore.kernel.org/lkml/cajz5v0h7ohr7ipj6ubgtlez238jzktshh93cye_gdx5j+zb...@mail.gmail.com/)
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2077470/+subscriptions
--
Mailing list: https://launchpad.net/~kernel-packages
Post to : [email protected]
Unsubscribe : https://launchpad.net/~kernel-packages
More help : https://help.launchpad.net/ListHelp
