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

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Date:   Wed, 16 Feb 2022 11:51:08 -0800
From:   srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Jonathan Corbet <corbet@....net>,
        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 Wed, 2022-02-16 at 19:44 +0100, Rafael J. Wysocki wrote:
> 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?
> 
Sure.

Thanks,
Srinivas

> > +
> > +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
> >