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Intel has released a new set of patches for its Linux drivers, promising to improve the performance of hybrid Alder Lake processors by optimizing the use of performance and efficiency cores. We’ve talked about the company’s new Thread Director technology in detail before, and you can see all the details here.

We mentioned that 12th Gen Core ‘Alder Lake’ processors perform better under Windows rather than Linux. Unlike Windows 11, Linux lacked proper support for Thread Director technology based on Advanced Hardware Feedback Interface (HFI), which allows two different types of kernels to be used properly.

According to Phoronix, currently the Linux kernel decides when to use performance or efficiency kernels using the ITMT/Turbo Boost Max 3.0 driver based on the information provided by the firmware. This is insufficient for the new architecture and the operating system has to opt for fast performance cores in most cases.

In contrast, HFI (Hardware Feedback Interface) can transmit the numerical performance and efficiency characteristics of each CPU core in the range of 0 – 255 to the operating system in real time. Intel explains it like this:

Intel Hardware Feedback Interface (HFI) provides information about the performance and energy efficiency of each CPU in the system. A table shared between hardware and operating system is being used. The contents of the table may be updated as a result of changes in the operating conditions of the system (for example, reaching a thermal limit) or as a result of the influence of external factors (for example, changes in thermal design power).

The information HFI provides is specified as numerical, unitless capabilities relative to other CPUs in the system. These abilities have a range of [0-255], where higher numbers represent higher abilities. Energy efficiency and performance are reported in separate capabilities. If a CPU’s performance or energy capabilities efficiency is 0, hardware recommends that you do not schedule any tasks on that CPU for performance, energy efficiency, or thermal reasons, respectively.

The kernel or userspace can use information from the HFI to change task layout and/or set power limits. This patch thread focuses on user space. The thermal notification framework has been expanded to transmit CPU capacity updates. Thus, a userspace daemon can bind workloads to specific CPUs and/or offline CPUs with zero capabilities.

The frequency of HFI updates is specific to each processor model. Some systems only have one HFI update at boot. Other systems may have an update every ten milliseconds.

New patches are still being tested and there is a possibility that they will be used by the upcoming Linux 5.17.


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