Intel P-State Driver Begins Preparing For Hybrid Processors (Alder Lake)

Written by Michael Larabel in Intel on 24 May 2021 at 01:27 PM EDT. 7 Comments
Intel's Linux preparations for Alder Lake -- and more broadly the concept of hybrid x86_64 CPUs with a mix of large Core and small Atom cores -- continues with the P-State CPU frequency scaling driver seeing new work to prepare for Intel's hybrid era.

The P-State CPU frequency scaling driver that is responsible for CPU frequency handling under Linux with modern Intel CPUs is being adapted to properly support hybrid architectures like the upcoming Alder Lake series.

The P-State driver is being adapted to deal with the possibility of hardware P-states (HWP) performance levels and CPU frequencies potentially being different between types of CPUs in a hybrid processor. Hybrid processor designs are a big shift in the driver handling especially for components like P-State. Even with current Intel CPUs, P-State running optimally and using an appropriate governor can make a big difference to the overall Linux system performance.

Queued into the Linux power management's "-next" Git branch is now this patch as well as another patch so far working to adapt P-State for hybrid designs with CPU-specific scaling factors. This initial P-State hybrid work will in turn appear in the Linux 5.14 mainline kernel this summer.

Intel 12th Gen Alder Lake processors are to feature a mix of high performance "Golden Cove" and high efficiency "Gracemont" cores. Besides how well the Linux CPU frequency scaling is handled, another important area we are waiting to see play out is around the scheduler. There has been some Linux kernel scheduler patches in preparing for Intel hybrid processors though it's not clear how prepared yet the mainline kernel is for Alder Lake especially with these processors to feature a "next-gen hardware scheduler." In any case, the open-source/Linux Alder Lake patches continue advancing and should have all of the core bits ironed out in time for these Alder Lake CPUs beginning to ship later this calendar year.
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