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<section id="user-guide-for-frequency-control">
<h1>User Guide for Frequency Control<a class="headerlink" href="#user-guide-for-frequency-control" title="Link to this heading"></a></h1>
<section id="description">
<h2>Description<a class="headerlink" href="#description" title="Link to this heading"></a></h2>
<p>GEOPM supports many interfaces to manipulate frequency. This guide provides
specifics on each of these interfaces including suggested use, implementation
nuances, and common pitfalls. Supported interfaces include:</p>
<ul class="simple">
<li><p>Direct frequency requests on CPU core/uncore and GPU</p></li>
<li><p>Hardware P-States (HWP) on CPU</p></li>
<li><p>Speed Select Technology - Core Priority (SST-CP) and Turbo Frequency (SST-TF)
on Intel CPUs ICX+</p></li>
</ul>
<p>GEOPM frequency decisions interact with the OS frequency drivers. This
interaction is detailed below. At a high level, frequency drivers may include
settings to drive frequency with the objective of achieving greater performance
or to lower power consumption, while other frequency driver settings may adhere
more strictly to user frequency requests. The interaction between driver and
GEOPM-driven frequency setting will vary depending upon the interface used.
Generally speaking, if a <code class="docutils literal notranslate"><span class="pre">userspace</span></code> governor is available on a given driver,
it is more likely to play nicely with GEOPM.</p>
<p>The ideal mechanism of frequency control depends of course on the use case and
priorities of the user. If performance repeatability is critical or the user
knows of ideal frequency settings, direct frequency requests are likely ideal.
If the user wishes to leverage as much of the power headroom as possible, SST
or HWP interfaces are useful. If the user also wishes the system to steer power
intelligently between cores and uncore based on internal telemetry, HWP will work
best. If computation on a given node is heterogeneous (i.e. some CPUs are given
more work or more critical work than others), SST features are likely to work
best.</p>
</section>
<hr class="docutils" />
<section id="linux-frequency-drivers">
<h2>Linux Frequency Drivers<a class="headerlink" href="#linux-frequency-drivers" title="Link to this heading"></a></h2>
<p>Linux CPU driver information can be found using <code class="docutils literal notranslate"><span class="pre">cpupower</span></code> as shown in the
example below. If the driver has a <code class="docutils literal notranslate"><span class="pre">userspace</span></code> CPU governor available, that will
generally not interfere with GEOPM frequency decisions.</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span>cpupower<span class="w"> </span>frequency-info
analyzing<span class="w"> </span>CPU<span class="w"> </span><span class="m">0</span>:
<span class="w"> </span>driver:<span class="w"> </span>acpi-cpufreq
<span class="w"> </span>CPUs<span class="w"> </span>which<span class="w"> </span>run<span class="w"> </span>at<span class="w"> </span>the<span class="w"> </span>same<span class="w"> </span>hardware<span class="w"> </span>frequency:<span class="w"> </span><span class="m">0</span>
<span class="w"> </span>CPUs<span class="w"> </span>which<span class="w"> </span>need<span class="w"> </span>to<span class="w"> </span>have<span class="w"> </span>their<span class="w"> </span>frequency<span class="w"> </span>coordinated<span class="w"> </span>by<span class="w"> </span>software:<span class="w"> </span><span class="m">0</span>
<span class="w"> </span>maximum<span class="w"> </span>transition<span class="w"> </span>latency:<span class="w"> </span><span class="m">10</span>.0<span class="w"> </span>us
<span class="w"> </span>hardware<span class="w"> </span>limits:<span class="w"> </span><span class="m">1000</span><span class="w"> </span>MHz<span class="w"> </span>-<span class="w"> </span><span class="m">2</span>.10<span class="w"> </span>GHz
<span class="w"> </span>available<span class="w"> </span>frequency<span class="w"> </span>steps:<span class="w"> </span><span class="m">2</span>.10<span class="w"> </span>GHz,<span class="w"> </span><span class="m">2</span>.10<span class="w"> </span>GHz,<span class="w"> </span><span class="m">2</span>.00<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.90<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.80<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.70<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.60<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.50<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.40<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.30<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.20<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1</span>.10<span class="w"> </span>GHz,<span class="w"> </span><span class="m">1000</span><span class="w"> </span>MHz
<span class="w"> </span>available<span class="w"> </span>cpufreq<span class="w"> </span>governors:<span class="w"> </span>ondemand<span class="w"> </span>performance<span class="w"> </span>schedutil
<span class="w"> </span>current<span class="w"> </span>policy:<span class="w"> </span>frequency<span class="w"> </span>should<span class="w"> </span>be<span class="w"> </span>within<span class="w"> </span><span class="m">1000</span><span class="w"> </span>MHz<span class="w"> </span>and<span class="w"> </span><span class="m">2</span>.10<span class="w"> </span>GHz.
<span class="w"> </span>The<span class="w"> </span>governor<span class="w"> </span><span class="s2">"performance"</span><span class="w"> </span>may<span class="w"> </span>decide<span class="w"> </span>which<span class="w"> </span>speed<span class="w"> </span>to<span class="w"> </span>use
<span class="w"> </span>within<span class="w"> </span>this<span class="w"> </span>range.
<span class="w"> </span>current<span class="w"> </span>CPU<span class="w"> </span>frequency:<span class="w"> </span>Unable<span class="w"> </span>to<span class="w"> </span>call<span class="w"> </span>hardware
<span class="w"> </span>current<span class="w"> </span>CPU<span class="w"> </span>frequency:<span class="w"> </span><span class="m">1</span>.02<span class="w"> </span>GHz<span class="w"> </span><span class="o">(</span>asserted<span class="w"> </span>by<span class="w"> </span>call<span class="w"> </span>to<span class="w"> </span>kernel<span class="o">)</span>
<span class="w"> </span>boost<span class="w"> </span>state<span class="w"> </span>support:
<span class="w"> </span>Supported:<span class="w"> </span>yes
<span class="w"> </span>Active:<span class="w"> </span>yes
</pre></div>
</div>
<p>When using the <code class="docutils literal notranslate"><span class="pre">userspace</span></code> or <code class="docutils literal notranslate"><span class="pre">performance</span></code> governor, the <code class="docutils literal notranslate"><span class="pre">acpi-cpufreq</span></code>
driver will not interfere with frequency decisions made by GEOPM. Other
governors may interfere with GEOPM frequency settings.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">intel_pstate</span></code> driver allows users access to <code class="docutils literal notranslate"><span class="pre">Hardware</span> <span class="pre">P-States</span></code> on
systems that support that feature. The <code class="docutils literal notranslate"><span class="pre">performance</span></code> governor is more likely
to adhere to GEOPM frequency decisions. The <code class="docutils literal notranslate"><span class="pre">powersave</span></code> governor tends to
lower CPU frequency when cores are running idle.</p>
</section>
<hr class="docutils" />
<section id="direct-frequency-requests">
<h2>Direct Frequency Requests<a class="headerlink" href="#direct-frequency-requests" title="Link to this heading"></a></h2>
<p>This is the most straightforward mechanism for selecting a specific frequency.</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span>geopmread<span class="w"> </span>CPU_FREQUENCY_STATUS<span class="w"> </span>core<span class="w"> </span><span class="m">0</span>
<span class="m">3400000000</span>
$<span class="w"> </span>geopmwrite<span class="w"> </span>MSR::PERF_CTL:FREQ<span class="w"> </span>core<span class="w"> </span><span class="m">0</span><span class="w"> </span><span class="m">1</span>.2e9
$<span class="w"> </span>geopmread<span class="w"> </span>CPU_FREQUENCY_STATUS<span class="w"> </span>core<span class="w"> </span><span class="m">0</span>
<span class="m">1200000000</span>
</pre></div>
</div>
<p>To set CPU uncore frequency, both min and max can be specified. To fix
uncore frequency to a specific value, set <code class="docutils literal notranslate"><span class="pre">CPU_UNCORE_FREQUENCY_MAX_CONTROL</span></code>
and <code class="docutils literal notranslate"><span class="pre">CPU_UNCORE_FREQUENCY_MIN_CONTROL</span></code> to the same value. Note that there is
no guarantee that the specified frequencies will be achieved, as the system may
be limited by hardware constraints.</p>
<section id="gpu-frequency">
<h3>GPU Frequency<a class="headerlink" href="#gpu-frequency" title="Link to this heading"></a></h3>
<p>Similar to CPU uncore frequency, GPU frequencies are specified via a min and max.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Some hardware has underlying logic that requires
<code class="docutils literal notranslate"><span class="pre">GPU_CORE_FREQUENCY_MIN_CONTROL</span></code> to always be less than
<code class="docutils literal notranslate"><span class="pre">GPU_CORE_FREQUENCY_MAX_CONTROL</span></code>. If you try to set the min control greater
than the max or the max control less than the min, it will result in a failure.
To avoid this issue, use the batch interface on geopmwrite.</p>
</div>
<p>Example: Set GPU 0 frequency to 1.0 GHz</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span><span class="nb">echo</span><span class="w"> </span>-e<span class="w"> </span><span class="s2">"GPU_CORE_FREQUENCY_MIN_CONTROL gpu 0 1e9 \n\</span>
<span class="s2"> GPU_CORE_FREQUENCY_MAX_CONTROL gpu 0 1e9"</span><span class="w"> </span><span class="se">\</span>
<span class="w"> </span><span class="p">|</span><span class="w"> </span>geopmwrite<span class="w"> </span>-f<span class="w"> </span>-
</pre></div>
</div>
<p>Example: Let GPU 1 frequency float between 800 MHz and 1.2 GHz</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span><span class="nb">echo</span><span class="w"> </span>-e<span class="w"> </span><span class="s2">"GPU_CORE_FREQUENCY_MIN_CONTROL gpu 1 8e8 \n\</span>
<span class="s2"> GPU_CORE_FREQUENCY_MAX_CONTROL gpu 1 1.2e9"</span><span class="w"> </span><span class="se">\</span>
<span class="w"> </span><span class="p">|</span><span class="w"> </span>geopmwrite<span class="w"> </span>-f<span class="w"> </span>-
</pre></div>
</div>
<p>Example: Set all GPU frequencies to use the full frequency range.</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span><span class="nb">echo</span><span class="w"> </span>-e<span class="w"> </span><span class="s2">"GPU_CORE_FREQUENCY_MIN_CONTROL board 0 \</span>
<span class="s2"> </span><span class="k">$(</span>geopmread<span class="w"> </span>GPU_CORE_FREQUENCY_MIN_AVAIL<span class="w"> </span>board<span class="w"> </span><span class="m">0</span><span class="k">)</span><span class="s2"> \</span>
<span class="s2"> \nGPU_CORE_FREQUENCY_MAX_CONTROL board 0 \</span>
<span class="s2"> </span><span class="k">$(</span>geopmread<span class="w"> </span>GPU_CORE_FREQUENCY_MAX_AVAIL<span class="w"> </span>board<span class="w"> </span><span class="m">0</span><span class="k">)</span><span class="s2">"</span><span class="w"> </span><span class="se">\</span>
<span class="w"> </span><span class="p">|</span><span class="w"> </span>geopmwrite<span class="w"> </span>-f<span class="w"> </span>-
</pre></div>
</div>
</section>
</section>
<hr class="docutils" />
<section id="intel-hardware-p-states-hwp">
<h2>Intel Hardware P-States (HWP)<a class="headerlink" href="#intel-hardware-p-states-hwp" title="Link to this heading"></a></h2>
<p>Users of Intel Hardware P-States (HWP) can set per-CPU or per-socket hints,
like desired energy-perf bias and suggested min/max frequency range. These
hints are ingested along with hardware telemetry and used to allow the CPU
to steer its own frequency setting dynamically. This allows the system to
respond more rapidly than the OS could to changes in workload behavior while
maintaining power requirements and desired user priority.</p>
<p>The main control mechanism with HWP is the per-core
<code class="docutils literal notranslate"><span class="pre">ENERGY_PERFORMANCE_PREFERENCE</span></code> or EPP. This is a value 0-15, where 0 is
higher performance and 15 is higher energy efficiency. The user can also
specify a frequency range per-core. Typically, a core with an EPP of 0 will
try to reach the higher end of the frequency range while a core with an EPP of
15 will try to remain at the lower end of its frequency range. If no frequency
range is specified, the core will have access to the full frequency range. Note
that setting min and max frequencies does not guarantee performance. Cores are still bound by
power/thermal/current limits and can be restricted beyond the minimum frequency
if required to do so by hardware limitations.</p>
<p><code class="docutils literal notranslate"><span class="pre">HWP_CAPABILITIES</span></code> includes frequencies of interest. The full frequency range
is [<code class="docutils literal notranslate"><span class="pre">LOWEST_PERFORMANCE</span></code>, <code class="docutils literal notranslate"><span class="pre">HIGHEST_PERFORMANCE</span></code>], and
<code class="docutils literal notranslate"><span class="pre">GUARANTEED_PERFORMANCE</span></code> is the frequency that all cores should be able to
reach simultaneously when running a typical power-hungry workload.</p>
<section id="using-geopm-with-hwp">
<h3>Using GEOPM with HWP<a class="headerlink" href="#using-geopm-with-hwp" title="Link to this heading"></a></h3>
<p>Enabling HWP on a system cannot be done using GEOPM. This is because a system
reset is required to disable it once it has been enabled. Thus, it interferes
with GEOPM’s save/restore capabilities.</p>
<p>The instructions below assume that the <code class="docutils literal notranslate"><span class="pre">intel_pstate</span></code> driver is active.</p>
<p>To check the status of HWP, use <code class="docutils literal notranslate"><span class="pre">HWP_ENABLE</span></code>. A return value of 0 indicates
HWP is disabled.</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span>geopmread<span class="w"> </span>MSR::PM_ENABLE:HWP_ENABLE<span class="w"> </span>package<span class="w"> </span><span class="m">0</span>
<span class="m">1</span>
</pre></div>
</div>
<p>Set a core’s HWP parameters (and check frequency to see the change reflected).
Here we will try to make core 0 be more power hungry and core 4 be more energy
efficient.</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span><span class="c1"># Check core 0 and 4 frequency (running idle)</span>
$<span class="w"> </span>geopmread<span class="w"> </span>CPU_FREQUENCY_STATUS<span class="w"> </span>cpu<span class="w"> </span><span class="m">0</span>
<span class="m">1000000000</span>
$<span class="w"> </span>geopmread<span class="w"> </span>CPU_FREQUENCY_STATUS<span class="w"> </span>cpu<span class="w"> </span><span class="m">4</span>
<span class="m">1000000000</span>
$<span class="w"> </span>geopmwrite<span class="w"> </span>MSR::HWP_REQUEST:ENERGY_PERFORMANCE_PREFERENCE<span class="w"> </span>cpu<span class="w"> </span><span class="m">4</span><span class="w"> </span><span class="m">15</span>
$<span class="w"> </span>geopmwrite<span class="w"> </span>MSR::HWP_REQUEST:MAXIMUM_PERFORMANCE<span class="w"> </span>cpu<span class="w"> </span><span class="m">4</span><span class="w"> </span><span class="m">1</span>.4e9
$<span class="w"> </span>geopmwrite<span class="w"> </span>MSR::HWP_REQUEST:ENERGY_PERFORMANCE_PREFERENCE<span class="w"> </span>cpu<span class="w"> </span><span class="m">0</span><span class="w"> </span><span class="m">0</span>
$<span class="w"> </span>geopmwrite<span class="w"> </span>MSR::HWP_REQUEST:MINIMUM_PERFORMANCE<span class="w"> </span>cpu<span class="w"> </span><span class="m">0</span><span class="w"> </span><span class="m">2</span>.2e9
$<span class="w"> </span>geopmread<span class="w"> </span>CPU_FREQUENCY_STATUS<span class="w"> </span>cpu<span class="w"> </span><span class="m">0</span>
<span class="m">2200000000</span>
$<span class="w"> </span>geopmread<span class="w"> </span>CPU_FREQUENCY_STATUS<span class="w"> </span>cpu<span class="w"> </span><span class="m">4</span>
<span class="m">1000000000</span>
</pre></div>
</div>
</section>
</section>
<hr class="docutils" />
<section id="intel-speed-select-technology-sst">
<h2>Intel Speed Select Technology (SST)<a class="headerlink" href="#intel-speed-select-technology-sst" title="Link to this heading"></a></h2>
<p>Intel Speed Select Technology (SST) includes a multitude of features for
heterogeneous power steering on CPUs. GEOPM supports SST-CP (Core Priority) and
SST-TF (Turbo Frequency). SST-CP is used to assign cores to different priority
buckets numbered 0-3, where 0 is highest priority and 3 is lowest priority for power
distribution. This feature uses similar controls as HWP. If the power budget is
exceeded, the frequency of lower priority cores is decreased more than the frequency
of higher priority cores.</p>
<p>SST-TF allows cores in high priority buckets 0/1 to achieve higher turbo
frequencies than is typically allowed by reducing the maximum turbo frequencies
of the lower priority cores. That way, even in power constrained scenarios
where all cores are active, cores with high priority work can be granted a
higher proportion of the power budget. This is achieved without violating any
hardware constraints, unlike overclocking.</p>
<p>These features are described in detail in the
<a class="reference internal" href="geopm_pio_sst.7.html"><span class="doc">geopm_pio_sst(7)</span></a> man page.</p>
</section>
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