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