Intel HFI To Premiere In Linux 5.18 For Improving Hybrid CPU Performance/Efficiency
Written by Michael Larabel in Intel on 6 February 2022 at 10:26 AM EST. 21 Comments
INTEL --
The Linux 5.18 kernel this spring is adding support for the Intel Hardware Feedback Interface (HFI, also talked about sometimes as the Enhanced Hardware Feedback interface - EHFI).

The Intel Hardware Feedback Interface is used for communicating performance and energy efficiency capabilities of individual CPU cores of the system. Linux in turn will use the Intel HFI data for making improved task placement decisions about where to place given work among the available CPU cores/threads.


Intel HFI is important for new Intel Alder Lake processors and forthcoming hybrid processor designs marketed as having "Thread Director" so the kernel has the appropriate knowledge for placing important tasks on the CPU cores with the greatest performance potential and placing background tasks and other less important work onto more energy efficient cores.


The Intel Hardware Feedback Interface isn't static (well, at least by the design, some platforms/firmware may only decide to program it at boot time but the HFI design is that it can dynamically change every "tens of milliseconds") but the feedback to the kernel/OS can change ultimately depending upon current thermal conditions and other factors.

Intel's Hardware Feedback Interface is what is already supported by Microsoft Windows 11 while now coming to Linux. Back in December I wrote more about this work in Intel HFI Code Revised For Improving Alder Lake's Hybrid Support On Linux. It was back in late 2020 when Intel first began documenting the Enhanced Hardware Feedback Interface. This will also be very important for future Intel processors.

The news this weekend is that the Intel HFI Linux kernel code has been merged into linux-pm's linux-next branch. With Linux power management subststem maintainer Rafael Wysocki (and Intel employee) having picked up the intel_hfi driver into the "-next" code, this basically signals it is ready for appearing in the next kernel cycle that will be Linux 5.18.

The Linux 5.18 merge window will formally happen around the end of March once v5.17 releases, but Linux 5.18 stable won't be out until late May or so. Unfortunately that puts this Intel HFI driver out of scope for shipping out-of-the-box in the spring Linux distribution releases (aside from the distros that are rolling release or like Fedora who ship major new kernels as stable release updates) but at least should be all baked for the autumn Linux distributions.

So look for the Intel HFI code appearing on Linux in the coming months for improving the kernel's scheduler task placement among their latest processors for better performance/efficiency.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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