Behavior of P core and E core in Ubuntu 22.04

Ubuntu 2022, the latest LTS of Ubuntu, was released on April 4, 21.

We have also verified the operation of Ubuntu 22.04, but we have confirmed a phenomenon that has not been seen so far, so I would like to inform you.

We used a machine with a Core i9-12900K CPU as a computer for verification work.
As many of you may already know, the core configuration of Intel CPUs has changed significantly from some products of this 12th generation Core series.Until now, the same core was installed multiple times according to the model, but from the corresponding model of this generation, performance such as clock was emphasized. "P core"And emphasized power saving performance"E-coreTwo different cores now coexist on the same package.

For P-core and E-core, the OS (kernel) manages allocations based on the operating status of the computer (software on it) and the nature of running threads.OS needs to be able to recognize P core and E core separately.

The initial kernel version of Ubuntu 22.04 that we verified is 5.15, but when we performed a calculation test that causes a high load with multiple threads on the OS running this version of the kernel,

-The core used is different each time it is executed.
-Threads running on the P core appear to be reassigned to the E core

Such behavior was confirmed.
If this behavior occurs when the P-core has enough capacity to operate, there is a concern that the resources of the higher-performance P-core that can be used will not be utilized and the CPU's original performance will not be exhibited.
This is probably due to incomplete support for the 5.15th generation Core series of version 12 Ubuntu kernels.
Since Ubuntu 22.04 is LTS, the adoption of the stable version of the kernel is prioritized.Therefore, it is possible that versions prior to the release of the 12th generation Core series have been adopted.

Ubuntu officially supports the 5.16th generation Core series in versions 12 and later, and as of 2022/6/5, the kernel of version 5.17 can be installed from the official Ubuntu repository.When the same test was performed after installing the version 5.17 kernel, it was confirmed that the behavior changed so that the P core was preferentially used in the situation where the number of threads was sufficient.

If the calculation speed is not reduced as expected when using the 22.04th generation Core series with Ubuntu 12 installed, the behavior may be improved by replacing the kernel with the updated version.
Incidentally,Kernel changes are not made without special reasonsTherefore, please use it at your own risk when you try it.It is also possible to perform the above procedures on the computer ordered by us before shipping, so please let us know when you purchase the computer.