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76 lines
2.9 KiB
76 lines
2.9 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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================================================== |
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Collaborative Processor Performance Control (CPPC) |
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================================================== |
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CPPC |
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==== |
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CPPC defined in the ACPI spec describes a mechanism for the OS to manage the |
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performance of a logical processor on a contiguous and abstract performance |
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scale. CPPC exposes a set of registers to describe abstract performance scale, |
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to request performance levels and to measure per-cpu delivered performance. |
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For more details on CPPC please refer to the ACPI specification at: |
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http://uefi.org/specifications |
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Some of the CPPC registers are exposed via sysfs under:: |
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/sys/devices/system/cpu/cpuX/acpi_cppc/ |
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for each cpu X:: |
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$ ls -lR /sys/devices/system/cpu/cpu0/acpi_cppc/ |
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/sys/devices/system/cpu/cpu0/acpi_cppc/: |
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total 0 |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 feedback_ctrs |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 highest_perf |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_freq |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_nonlinear_perf |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 lowest_perf |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 nominal_freq |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 nominal_perf |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 reference_perf |
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-r--r--r-- 1 root root 65536 Mar 5 19:38 wraparound_time |
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* highest_perf : Highest performance of this processor (abstract scale). |
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* nominal_perf : Highest sustained performance of this processor |
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(abstract scale). |
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* lowest_nonlinear_perf : Lowest performance of this processor with nonlinear |
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power savings (abstract scale). |
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* lowest_perf : Lowest performance of this processor (abstract scale). |
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* lowest_freq : CPU frequency corresponding to lowest_perf (in MHz). |
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* nominal_freq : CPU frequency corresponding to nominal_perf (in MHz). |
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The above frequencies should only be used to report processor performance in |
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frequency instead of abstract scale. These values should not be used for any |
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functional decisions. |
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* feedback_ctrs : Includes both Reference and delivered performance counter. |
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Reference counter ticks up proportional to processor's reference performance. |
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Delivered counter ticks up proportional to processor's delivered performance. |
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* wraparound_time: Minimum time for the feedback counters to wraparound |
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(seconds). |
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* reference_perf : Performance level at which reference performance counter |
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accumulates (abstract scale). |
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Computing Average Delivered Performance |
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======================================= |
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Below describes the steps to compute the average performance delivered by |
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taking two different snapshots of feedback counters at time T1 and T2. |
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T1: Read feedback_ctrs as fbc_t1 |
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Wait or run some workload |
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T2: Read feedback_ctrs as fbc_t2 |
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:: |
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delivered_counter_delta = fbc_t2[del] - fbc_t1[del] |
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reference_counter_delta = fbc_t2[ref] - fbc_t1[ref] |
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delivered_perf = (refernce_perf x delivered_counter_delta) / reference_counter_delta
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