1.. SPDX-License-Identifier: GPL-2.0 2 3================================================== 4Collaborative Processor Performance Control (CPPC) 5================================================== 6 7.. _cppc_sysfs: 8 9CPPC 10==== 11 12CPPC defined in the ACPI spec describes a mechanism for the OS to manage the 13performance of a logical processor on a contiguous and abstract performance 14scale. CPPC exposes a set of registers to describe abstract performance scale, 15to request performance levels and to measure per-cpu delivered performance. 16 17For more details on CPPC please refer to the ACPI specification at: 18 19http://uefi.org/specifications 20 21Some of the CPPC registers are exposed via sysfs under:: 22 23 /sys/devices/system/cpu/cpuX/acpi_cppc/ 24 25for each cpu X:: 26 27 $ ls -lR /sys/devices/system/cpu/cpu0/acpi_cppc/ 28 /sys/devices/system/cpu/cpu0/acpi_cppc/: 29 total 0 30 -r--r--r-- 1 root root 65536 Mar 5 19:38 feedback_ctrs 31 -r--r--r-- 1 root root 65536 Mar 5 19:38 highest_perf 32 -r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_freq 33 -r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_nonlinear_perf 34 -r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_perf 35 -r--r--r-- 1 root root 65536 Mar 5 19:38 nominal_freq 36 -r--r--r-- 1 root root 65536 Mar 5 19:38 nominal_perf 37 -r--r--r-- 1 root root 65536 Mar 5 19:38 reference_perf 38 -r--r--r-- 1 root root 65536 Mar 5 19:38 wraparound_time 39 40* highest_perf : Highest performance of this processor (abstract scale). 41* nominal_perf : Highest sustained performance of this processor 42 (abstract scale). 43* lowest_nonlinear_perf : Lowest performance of this processor with nonlinear 44 power savings (abstract scale). 45* lowest_perf : Lowest performance of this processor (abstract scale). 46 47* lowest_freq : CPU frequency corresponding to lowest_perf (in MHz). 48* nominal_freq : CPU frequency corresponding to nominal_perf (in MHz). 49 The above frequencies should only be used to report processor performance in 50 frequency instead of abstract scale. These values should not be used for any 51 functional decisions. 52 53* feedback_ctrs : Includes both Reference and delivered performance counter. 54 Reference counter ticks up proportional to processor's reference performance. 55 Delivered counter ticks up proportional to processor's delivered performance. 56* wraparound_time: Minimum time for the feedback counters to wraparound 57 (seconds). 58* reference_perf : Performance level at which reference performance counter 59 accumulates (abstract scale). 60 61 62Computing Average Delivered Performance 63======================================= 64 65Below describes the steps to compute the average performance delivered by 66taking two different snapshots of feedback counters at time T1 and T2. 67 68 T1: Read feedback_ctrs as fbc_t1 69 Wait or run some workload 70 71 T2: Read feedback_ctrs as fbc_t2 72 73:: 74 75 delivered_counter_delta = fbc_t2[del] - fbc_t1[del] 76 reference_counter_delta = fbc_t2[ref] - fbc_t1[ref] 77 78 delivered_perf = (refernce_perf x delivered_counter_delta) / reference_counter_delta 79