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| -rw-r--r-- | Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst | 60 |
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diff --git a/Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst b/Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst new file mode 100644 index 000000000000..09169d935835 --- /dev/null +++ b/Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst @@ -0,0 +1,60 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + +============================== +Intel Uncore Frequency Scaling +============================== + +:Copyright: |copy| 2022 Intel Corporation + +:Author: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> + +Introduction +------------ + +The uncore can consume significant amount of power in Intel's Xeon servers based +on the workload characteristics. To optimize the total power and improve overall +performance, SoCs have internal algorithms for scaling uncore frequency. These +algorithms monitor workload usage of uncore and set a desirable frequency. + +It is possible that users have different expectations of uncore performance and +want to have control over it. The objective is similar to allowing users to set +the scaling min/max frequencies via cpufreq sysfs to improve CPU performance. +Users may have some latency sensitive workloads where they do not want any +change to uncore frequency. Also, users may have workloads which require +different core and uncore performance at distinct phases and they may want to +use both cpufreq and the uncore scaling interface to distribute power and +improve overall performance. + +Sysfs Interface +--------------- + +To control uncore frequency, a sysfs interface is provided in the directory: +`/sys/devices/system/cpu/intel_uncore_frequency/`. + +There is one directory for each package and die combination as the scope of +uncore scaling control is per die in multiple die/package SoCs or per +package for single die per package SoCs. The name represents the +scope of control. For example: 'package_00_die_00' is for package id 0 and +die 0. + +Each package_*_die_* contains the following attributes: + +``initial_max_freq_khz`` + Out of reset, this attribute represent the maximum possible frequency. + This is a read-only attribute. If users adjust max_freq_khz, + they can always go back to maximum using the value from this attribute. + +``initial_min_freq_khz`` + Out of reset, this attribute represent the minimum possible frequency. + This is a read-only attribute. If users adjust min_freq_khz, + they can always go back to minimum using the value from this attribute. + +``max_freq_khz`` + This attribute is used to set the maximum uncore frequency. + +``min_freq_khz`` + This attribute is used to set the minimum uncore frequency. + +``current_freq_khz`` + This attribute is used to get the current uncore frequency. |