Linux 5.20 To Help Ensure Intel CPUs With AMX Can Hit Their Lowest Power Idle States

In addition to new kernel code and updated firmware fixing a power management issue for Xeon Scalable "Sapphire Rapids" where C1 and C1E power states were mutually exclusive, another important Sapphire Rapids power management improvement is on the way with the upcoming Linux 5.20 kernel cycle.

Queued into TIP's x86/fpu branch is the previously covered work on ensuring the AMX state is prepared for low-power CPU idle. With Sapphire Rapids introducing the new AMX (Advanced Matrix Extensions) at least for the Sapphire Rapids generation, non-initialized AMX register state can lead to C-state demotion from C6 to C1E.

Advanced Matrix Extensions (AMX) debut with Sapphire Rapids. Intel engineers remain busy squaring away the AMX support from the Linux kernel up through the compiler toolchains.

This is the work originally covered back in May for Linux patches improving power management for AMX servers. Ensuring cores can hit the lowest possible low-power idle state with the Intel_Idle driver is important for ensuring a higher turbo frequency budget for other non-idle CPU cores.

The issue of non-initialized AMX state causing possible C-state demotion is being treated as an implementation specific issue of Sapphire Rapids with the queued Linux kernel code. The patches for handling this are in TIP's x86/fpu branch ahead of the Linux 5.20 merge window opening up next week.