Linux 7.3 To Allow Tuning AMD P-State Dynamic EPP With Per CPU Core Granularity

Sent out last night was the last batch of planned AMD P-State driver feature improvements targeting the upcoming Linux 7.3 merge window. Most notable for the AMD P-State driver updates for Linux 7.3 is a rework to the Dynamic Energy Performance Preference (EPP) handling. Dynamic EPP is an existing opt-in AMD P-State driver feature that allows for the kernel to autonomously change the EPP operating mode. With the Linux 7.3 kernel, rather than Dynamic EPP being a single global switch, the functionality can now be controlled on a per-CPU core basis. The patch from AMD Linux engineer K Prateek Nayak explains: "Convert the global "dynamic_epp" toggle into a per-CPU "energy_performance_preference" mode "dynamic" that allows toggling the functionality of "dynamic_epp" at a per-CPU level. Instead of being a system-wide toggle, users can opt into the functionality of dynamic EPP on a per-CPU basis by switching to the powersave governor and selecting the "dynamic" mode from the available performance preferences. Unlike the previous implementation that had to check for driver mode before toggling on the functionality, block writes to certain sysfs files, potentially disallow policy change, etc. the per-CPU toggle fits naturally into the intended design and provides more granular control to the user. The dynamic_epp file is now redundant as the option to toggle it on is controlled via energy_performance_preference, and the dynamic_epp file will be removed in the subsequent commit." This pull request of AMD P-State updates to be merged to the Linux power management subsystem branch has that dynamic EPP rework and dropping of the existing global "amd_dynamic_epp" module parameter and "dynamic_epp" sysfs nodes. That pull also has a patch to now set the min_limit_freq value based on the bios_min_perf value, as the existing behavior was found to be sub-optimal for users who have profiled their workloads at different operating frequencies and in turn manually tuned the bios_min_perf setting.