Added documentation to configure uncore frequency limits in Intel
Xeon processors.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
---
v2
As suggested removed "===" (chapter) for Introduction and added two sections
"Introduction" and "Sysfs interface".
.../pm/intel_uncore_frequency_scaling.rst | 59 +++++++++++++++++++
.../admin-guide/pm/working-state.rst | 1 +
2 files changed, 60 insertions(+)
create mode 100644 Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst
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..a55cf68d77df
--- /dev/null
+++ b/Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst
@@ -0,0 +1,59 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. include:: <isonum.txt>
+
+==============================
+Intel Uncore Frequency Scaling
+==============================
+
+:Copyright: |copy| 2022 Intel Corporation
+
+:Author: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
+
+Introduction
+------------
+
+Uncore can consume significant amount of power in Intel's Xeon servers based
+on the workload characteristics. To optimize total power and improve overall
+performance, SoC has an internal algorithm 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 set scaling min/max
+frequencies using cpufreq sysfs to improve compute performance. Users may have
+some latency sensitive workload where they do not want any change to uncore
+frequency. Also, users may have workload which requires different core and
+uncore performance at distinct phases and they want to use both cpufreq and
+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 dies/package SoC or per
+package for single die per package SoC. The name represents the
+scope of control. For example: 'package_00_die_00' is for package id 0 and
+die 0 in it.
+
+Each package_*_die_* contains 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.
diff --git a/Documentation/admin-guide/pm/working-state.rst b/Documentation/admin-guide/pm/working-state.rst
index 5d2757e2de65..ee45887811ff 100644
--- a/Documentation/admin-guide/pm/working-state.rst
+++ b/Documentation/admin-guide/pm/working-state.rst
@@ -15,3 +15,4 @@ Working-State Power Management
cpufreq_drivers
intel_epb
intel-speed-select
+ intel_uncore_frequency_scaling
--
2.34.1
