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