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Jason Andryuk
99c4570f82
From the Intel SDM: "Hardware-Controlled Performance States (HWP), which autonomously selects performance states while utilizing OS supplied performance guidance hints." Enable HWP to run in autonomous mode by poking the correct MSRs. HWP is disabled by default, and cpufreq=hwp enables it. cpufreq= parsing is expanded to allow cpufreq=hwp;xen. This allows trying HWP and falling back to xen if not available. Only hwp and xen are supported for this fallback feature. hdc is a sub-option under hwp (i.e. cpufreq=hwp,hdc=0) as is verbose. There is no interface to configure - xen_sysctl_pm_op/xenpm will be extended to configure in subsequent patches. It will run with the default values, which should be the default 0x80 (out of 0x0-0xff) energy/performance preference. Unscientific powertop measurement of an mostly idle, customized OpenXT install: A 10th gen 6-core laptop showed battery discharge drop from ~9.x to ~7.x watts. A 8th gen 4-core laptop dropped from ~10 to ~9 Power usage depends on many factors, especially display brightness, but this does show a power saving in balanced mode when CPU utilization is low. HWP isn't compatible with an external governor - it doesn't take explicit frequency requests. Therefore a minimal internal governor, hwp, is also added as a placeholder. While adding to the xen-command-line.pandoc entry, un-nest verbose from minfreq. They are independent. With cpufreq=hwp,verbose, HWP prints processor capabilities that are not used by the code, like HW_FEEDBACK. This is done because otherwise there isn't a convenient way to query the information. Xen doesn't use the HWP interrupt, so it is disabled like in the Linux pstate driver. Signed-off-by: Jason Andryuk <jandryuk@gmail.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>