Add a file to describe the CPPC sysfs interface and steps to compute average delivered performance using the feedback counters. Signed-off-by: Prashanth Prakash <pprakash@xxxxxxxxxxxxxx> --- Documentation/acpi/cppc_sysfs.txt | 66 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) create mode 100644 Documentation/acpi/cppc_sysfs.txt diff --git a/Documentation/acpi/cppc_sysfs.txt b/Documentation/acpi/cppc_sysfs.txt new file mode 100644 index 0000000..9fae408 --- /dev/null +++ b/Documentation/acpi/cppc_sysfs.txt @@ -0,0 +1,66 @@ + + Collaborative Processor Performance Control (CPPC) + +CPPC defined in ACPI spec describes a mechanism for OSPM to manage the +performance of a logical processor on a contigious and abstract performance +scale. CPPC exposes different 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 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 -- Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
