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author | Prashanth Prakash <pprakash@codeaurora.org> | 2018-04-04 12:14:53 -0600 |
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committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2018-04-24 12:33:28 +0200 |
commit | b382bf885269bffaa8444a9310db680f2f0f4151 (patch) | |
tree | 1e2196f3c77e1eb4ce6417abe974b17a46af272b | |
parent | 256f19d212f260c955a90a0efc7753e11b18e34c (diff) | |
download | op-kernel-dev-b382bf885269bffaa8444a9310db680f2f0f4151.zip op-kernel-dev-b382bf885269bffaa8444a9310db680f2f0f4151.tar.gz |
ACPI / CPPC: Document CPPC sysfs interface
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@codeaurora.org>
[ rjw: Minor adjustments ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
-rw-r--r-- | Documentation/acpi/cppc_sysfs.txt | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/Documentation/acpi/cppc_sysfs.txt b/Documentation/acpi/cppc_sysfs.txt new file mode 100644 index 0000000..f20fb44 --- /dev/null +++ b/Documentation/acpi/cppc_sysfs.txt @@ -0,0 +1,69 @@ + + 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 |