Similar to the Autonomous Performance Level Selection and Energy Performance Preference (EPP) support already found within the Intel P-State and AMD P-State CPU frequency scaling drivers for their modern processors, NVIDIA engineers are working on similar support for the CPPC CPUFreq driver that can benefit their Grace processor.
Sent out this week were a set of patches for wiring up Autonomous Selection mode in cppc_cpufreq for complying with the ACPI Collaborative Processor Performance Control (CPPC) specifications. Sumit Gupta of NVIDIA explains in the patch series:
“It adds a new ‘cppc_cpufreq_epp’ instance of the ‘cppc_cpufreq’ driver for supporting the Autonomous Performance Level Selection and Energy Performance Preference (EPP). Autonomous selection will get enabled during boot if ‘cppc_auto_sel’ boot argument is passed or the ‘Autonomous Selection Enable’ register is already set before kernel boot. When enabled, the hardware is allowed to autonomously select the CPU frequency within the min and max perf boundaries using the Engergy Performance Preference hints. The EPP values range from ‘0x0′(performance preference) to ‘0xFF’ (energy efficiency preference).
It also exposes the acpi_cppc sysfs nodes to update the epp, auto_sel and {min|max_perf} registers for changing the hints to hardware for Autonomous selection.
In a followup patch, plan to add support to dynamically switch the cpufreq driver instance from ‘cppc_cpufreq_epp’ to ‘cppc_cpufreq’ and vice-versa without reboot.”
This will allow more fine-tuning of power/performance preferences on NVIDIA Grace systems (like the GPTshop GH200 hardware) and other platforms using the CPPC CPUFreq driver while supporting the ACPI CPPC specifications.
More details for those interested in the work via this patch series.
