Last week saw a number of changes to the power management module of the Linux 5.18 kernel in development, including significant improvements for AMD and Intel processors. In addition to Intel’s Hardware Feedback Interface (HFI) support for sending through the thermal subsystem, the Linux 5.18 power management update also has some notable changes.
Intel’s Idle Linux driver (intel_idle) now provides native support for the upcoming Xeon Sapphire Rapids CPUs. On these upcoming server CPUs, the OS now also has the ability to better control C-States. With the change of the intel_idle parameter, Sapphire Rapids also brings optimizations for the core C6 state.
Meanwhile, Intel’s P-state driver will now use the default Energy Performance Preference (EPP) provided by the firmware. So far, Intel P-state has provided Alder Lake with a hardcoded EPP default in an attempt to ensure that the maximum single-core turbo frequency is reached out of the box, but going forward the Linux kernel will respect the firmware’s EPP default. If the firmware does not provide a default EPP value, the hardcoded value will be used.
On the AMD CPU side, the CPUPower tool in the kernel source tree now supports running with the AMD P-state driver. Linux 5.17 introduced the AMD P-state driver as a replacement for ACPI CPUFreq on Zen 2 systems and newer, and the CPUPower changes are now in place to work in the case of amd_pstate, in addition to new tracing tools for Driven by AMD P-State.
Virtualized Linux guests will now also get ACPI S4 hardware signatures by default, see the Power Management section for full changes this cycle:
Intel’s PM/ACPI maintainer, Rafael Wysocki, also submitted an ACPI update at the same time last week. A new Arm Generic Diagnostic Dump and Reset device driver was introduced, providing support for new hardware and other general ACPI changes.