.. SPDX-License-Identifier: GPL-2.0 ================================================== Collaborative Processor Performance Control (CPPC) ================================================== .. _cppc_sysfs: CPPC ==== CPPC defined in the ACPI spec describes a mechanism for the OS to manage the performance of a logical processor on a contiguous and abstract performance scale. CPPC exposes a set of registers to describe abstract performance scale, to request performance levels and to measure per-cpu delivered performance. For more details on CPPC please refer to the ACPI specification at: http://uefi.org/specifications Some of the CPPC registers are exposed via sysfs under:: /sys/devices/system/cpu/cpuX/acpi_cppc/ for each cpu X:: $ ls -lR /sys/devices/system/cpu/cpu0/acpi_cppc/ /sys/devices/system/cpu/cpu0/acpi_cppc/: total 0 -r--r--r-- 1 root root 65536 Mar 5 19:38 feedback_ctrs -r--r--r-- 1 root root 65536 Mar 5 19:38 highest_perf -r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_freq -r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_nonlinear_perf -r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_perf -r--r--r-- 1 root root 65536 Mar 5 19:38 nominal_freq -r--r--r-- 1 root root 65536 Mar 5 19:38 nominal_perf -r--r--r-- 1 root root 65536 Mar 5 19:38 reference_perf -r--r--r-- 1 root root 65536 Mar 5 19:38 wraparound_time * highest_perf : Highest performance of this processor (abstract scale). * nominal_perf : Highest sustained performance of this processor (abstract scale). * lowest_nonlinear_perf : Lowest performance of this processor with nonlinear power savings (abstract scale). * lowest_perf : Lowest performance of this processor (abstract scale). * lowest_freq : CPU frequency corresponding to lowest_perf (in MHz). * nominal_freq : CPU frequency corresponding to nominal_perf (in MHz). The above frequencies should only be used to report processor performance in frequency instead of abstract scale. These values should not be used for any functional decisions. * feedback_ctrs : Includes both Reference and delivered performance counter. Reference counter ticks up proportional to processor's reference performance. Delivered counter ticks up proportional to processor's delivered performance. * wraparound_time: Minimum time for the feedback counters to wraparound (seconds). * reference_perf : Performance level at which reference performance counter accumulates (abstract scale). Computing Average Delivered Performance ======================================= Below describes the steps to compute the average performance delivered by taking two different snapshots of feedback counters at time T1 and T2. T1: Read feedback_ctrs as fbc_t1 Wait or run some workload T2: Read feedback_ctrs as fbc_t2 :: delivered_counter_delta = fbc_t2[del] - fbc_t1[del] reference_counter_delta = fbc_t2[ref] - fbc_t1[ref] delivered_perf = (reference_perf x delivered_counter_delta) / reference_counter_delta