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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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==================================================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