linux-kernel - [PATCH] Documentation: admin-guide: pm: Document uncore frequency scaling

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Message-Id: <20220207191307.2903314-1-srinivas.pandruvada@linux.intel.com>
Date:   Mon,  7 Feb 2022 11:13:07 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     corbet@....net, rafael@...nel.org, hdegoede@...hat.com,
        markgross@...nel.org
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: [PATCH] Documentation: admin-guide: pm: Document uncore frequency scaling

Added documentation to configure uncore frequency limits in Intel
Xeon processors.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
---
Resent by adding linux-pm@...r.kernel.org

 .../pm/intel_uncore_frequency_scaling.rst     | 56 +++++++++++++++++++
 .../admin-guide/pm/working-state.rst          |  1 +
 2 files changed, 57 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..b3519560594b
--- /dev/null
+++ b/Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst
@@ -0,0 +1,56 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. include:: <isonum.txt>
+
+==============================
+Intel Uncore Frequency Scaling
+==============================
+
+:Copyright: |copy| 2022 Intel Corporation
+
+:Author: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
+
+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.
+
+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