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From: Bruce Richardson <bruce.richardson@intel.com>
To: dev@dpdk.org
Cc: david.marchand@redhat.com, mb@smartsharesystems.com,
stephen@networkplumber.org, Bruce Richardson <bruce.richardson@intel.com>
Subject: [PATCH v3 3/4] doc: provide examples of using lcores EAL parameter
Date: Fri, 2 May 2025 16:11:33 +0100
Message-ID: <20250502151134.536799-4-bruce.richardson@intel.com>
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The "--lcores" EAL parameter has a very powerful syntax that can be used
to provide precise control over lcore mappings. The docs however, only
provided a minimal description of what it can do. Augment the docs by
providing some examples of use of the option, and what the resulting
core mappings would be.
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
---
doc/guides/linux_gsg/eal_args.include.rst | 27 +++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/doc/guides/linux_gsg/eal_args.include.rst b/doc/guides/linux_gsg/eal_args.include.rst
index 01fe6a3006..d530215784 100644
--- a/doc/guides/linux_gsg/eal_args.include.rst
+++ b/doc/guides/linux_gsg/eal_args.include.rst
@@ -23,6 +23,33 @@ Lcore-related options
The grouping ``()`` can be omitted for single element group.
The ``@`` can be omitted if cpus and lcores have the same value.
+ Examples:
+
+ ``--lcores=1-3``: Run threads on physical CPUs 1, 2 and 3,
+ with each thread having the same lcore id as the physical CPU id.
+
+ ``--lcores=1@(1,2)``: Run a single thread with lcore id 1,
+ but with that thread bound to both physical CPUs 1 and 2,
+ so it can run on either, as determined by the operating system.
+
+ ``--lcores='1@31,2@32,3@33'``: Run threads having internal lcore ids of 1, 2 and 3,
+ but with the threads being bound to physical CPUs 31, 32 and 33 respectively.
+
+ ``--lcores='(1-3)@(31-33)'``: Run three threads with lcore ids 1, 2 and 3.
+ Unlike the previous example above,
+ each of these threads is not bound to one specific physical CPU,
+ but rather, all three threads are instead bound to the three physical CPUs 31, 32 and 33.
+ This means that each of the three threads can move between the physical CPUs 31-33,
+ as decided by the OS as the application runs.
+
+ ``--lcores=(1-3)@20``: Run three threads, with lcore ids 1, 2 and 3,
+ where all three threads are bound to (can only run on) physical CPU 20.
+
+.. Note::
+ Binding multiple DPDK lcores to a single physical CPU can cause problems with poor performance
+ or deadlock when using DPDK rings or memory pools or spinlocks.
+ Such a configuration should only be used with care.
+
.. Note::
At a given instance only one core option ``--lcores``, ``-l`` or ``-c`` can
be used.
--
2.45.2