Linux 5.4 Power Management Updates Sent In But Without AMD CPPC Changes
This time around the power management work isn't particularly exciting with no breakthroughs for the Intel P-State driver, no major changes to the other prominent CPUFreq drivers/governors, and no AMD CPPC support for their new processors.
Following the AMD Ryzen 3000 series launch, AMD engineers did propose a new CPUfreq CPPC driver for Zen 2 CPUs. There were some benefits to that code but upstream kernel developers took issue with some elements to that design. As a result, that new AMD Collaborative Processor Performance Control driver isn't going to land with the Linux 5.4 kernel. AMD will likely need to rework that code to better jive with the ongoing work to the Schedutil governor and other comments made by upstream. We'll cross our fingers that AMD has some improvements ready to go for Linux 5.5, which will see its merge window open in November but not release as stable until early 2020.
As for what did make it for Linux 5.4, some of the power management highlights include:
- System suspend stats are now exposed via sysfs.
- A haltpoll CPU idle driver and governor were added for virtualized guests to do guest-side polling in the idle loop.
- Various CPUfreq driver updates for different ARM SoCs from the Sun50i to MT8183/MT8516 to i.MX8MN to Qualcomm. There is also a new devfreq driver for the NVIDIA Tegra20.
The ACPI updates have a fix for the ACPI Low-Power Subsystem (LPSS) support for Intel SoCs and other fixes.