ACPI 6.1, CPUFreq Schedutil Provide Power Fun For Linux 4.7

Written by Michael Larabel in Linux Kernel on 16 May 2016 at 09:57 PM EDT. 1 Comment
The latest fun stuff worth mentioning for the Linux 4.7 kernel merge window are the ACPI and power management updates.

Rafael Wysocki sent in the ACPI and PM updates on Monday and they are once again on the heavy side. First off, the power management updates do include the new "Schedutil" governor for CPUFreq that we've been looking forward to since the earlier prep changes in Linux 4.6. This governor makes use of the kernel's scheduler utilization data to make better decisions about changing the CPU frequency state. Rafael explained further in the pull request message:
There are two main differences between it and the existing governors. First, it uses the information provided by the scheduler directly for making its decisions, so it doesn't have to track anything by itself. Second, it can invoke drivers (supporting that feature) to adjust CPU performance right away without having to spawn work items to be executed in process context or similar. Currently, the acpi-cpufreq driver is the only one supporting that mode of operation, but then it is used on a large number of systems.

The "schedutil" governor as included here is very simple and mostly regarded as a foundation for future work on the integration of the scheduler with CPU power management (in fact, there is work in progress on top of it already). Nevertheless it works and the preliminary results obtained with it are encouraging.

The power management pull for Linux 4.7 also has changes for CPU frequency management on ARM, the P-State driver now respects frequency limits set by the platform firmware, various CPUFreq driver fixes, Intel Broxton support within the intel_idle driver, core fixes and clean-ups, Intel Kabylake support in the RAPL / power capping driver, and various other power-related updates. More details via this kernel mailing list message.

With the ACPI space, there's now ACPI 6.1 support in ACPICA. There's also a new ACPI Generic Devent Device driver for ACPI 6.1 and a new INT3406 thermal driver. Various other changes here too. Details here.

The ACPI 6.1 specification was published back in January. The Generic Event Device from ACPI 6.1 adds support for handling platform interrupts in ACPI ASL statements.
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