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

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Date:   Wed, 16 Feb 2022 19:44:23 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     Jonathan Corbet <corbet@....net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] Documentation: admin-guide: pm: Document uncore frequency scaling

On Mon, Feb 7, 2022 at 8:13 PM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> 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
> +===========================================

There are no other sections in this file, so can the section header
above be dropped?

> +
> +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
>