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- Collaborative Processor Performance Control (CPPC)
- CPPC defined in the ACPI spec describes a mechanism for the OS to manage the
- performance of a logical processor on a contigious and abstract performance
- scale. 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
- freqency 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 by taking
- 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 = (refernce_perf x delivered_counter_delta) / reference_counter_delta
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