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DOCTEAM-2059 Modified values and explanation for sched_min_granularity_ns and sched_wakeup_granularity_ns #1911

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DOCTEAM-2059 Modified values and explanation for sched_min_granularity_ns and sched_wakeup_granularity_ns #1911

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8 changes: 8 additions & 0 deletions xml/book_tuning.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -143,6 +143,14 @@
<title>Kernel tuning</title>
<info>
<revhistory xml:id="rh-tuning-part-kerneltuning">
<revision>
<date>2026-03-31</date>
<revdescription>
<para>
Modified values and explanation for sched_min_granularity_ns and sched_wakeup_granularity_ns.
</para>
</revdescription>
</revision>
<revision>
<date>2024-03-12</date>
<revdescription>
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18 changes: 9 additions & 9 deletions xml/tuning_taskscheduler.xml
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Expand Up @@ -615,22 +615,22 @@ kernel.sched_wakeup_granularity_ns = 10000000</screen>
<term><systemitem>sched_min_granularity_ns</systemitem></term>
<listitem>
<para>
Minimal preemption granularity for CPU bound tasks. See
<systemitem>sched_latency_ns</systemitem> for details. The
default value is <literal>4000000</literal> (ns).
Minimal preemption granularity for CPU bound tasks. See
<systemitem>sched_latency_ns</systemitem> for details. The default value is calculated
as <literal>750000 * (1 + ilog(ncpus))</literal> nanoseconds, where
<literal>ilog(ncpus)</literal> is the integer <literal>base-2</literal> logarithm of
the number of online CPUs. For example, on a 2-CPU system the default is
<literal>1500000</literal> ns. The actual value reported by
<systemitem>sysctl</systemitem> is therefore machine-specific and varies with CPU count
and the value of <literal>sched_tunable_scaling</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><systemitem>sched_wakeup_granularity_ns</systemitem></term>
<listitem>
<para>
The wake-up preemption granularity. Increasing this variable
reduces wake-up preemption, reducing disturbance of compute bound
tasks. Lowering it improves wake-up latency and throughput for
latency critical tasks, particularly when a short duty cycle load
component must compete with CPU bound components. The default
value is <literal>2500000</literal> (ns).
The wake-up preemption granularity. Increasing this variable reduces wake-up preemption, reducing disturbance of compute bound tasks. Lowering it improves wake-up latency and throughput for latency critical tasks, particularly when a short duty cycle load component must compete with CPU bound components. The default value is calculated as <literal>1000000 * (1 + ilog(ncpus))</literal> nanoseconds, where <literal>ilog(ncpus)</literal> is the integer <literal>base-2</literal> logarithm of the number of online CPUs. For example, on a 2-CPU system the default is <literal>2000000</literal> ns. The actual value reported by <systemitem>sysctl</systemitem> is therefore machine-specific and varies with CPU count and the value of <literal>sched_tunable_scaling</literal>.
</para>
<warning>
<title>Setting the right wake-up granularity value</title>
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