.. 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 theperformance of a logical processor on a contiguous and abstract performancescale. 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 bytaking 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