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