On 09/09/2025 13:29, Eelco Chaudron wrote:
>
>
> On 8 Sep 2025, at 17:26, Kevin Traynor via dev wrote:
>
>> Add some more details about dpdk-lcore-mask and remove
>> the recommendation to use it.
>>
>> Signed-off-by: Kevin Traynor <ktray...@redhat.com>
>> ---
>> vswitchd/vswitch.xml | 17 ++++++++++++-----
>> 1 file changed, 12 insertions(+), 5 deletions(-)
>>
>> diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
>> index 332d8890d..25b0989ac 100644
>> --- a/vswitchd/vswitch.xml
>> +++ b/vswitchd/vswitch.xml
>> @@ -335,11 +335,18 @@
>> </p>
>> <p>
>> - For performance reasons, it is best to set this to a single core
>> on
>> - the system, rather than allow lcore threads to float.
>> + The lowest set core will be assigned in DPDK as the DPDK main
>> thread.
>> + Other set bits will be assigned by DPDK as DPDK worker threads.
>> + As OVS implements it's own threading for the datapath (see
>> + <ref column="other_config" key="pmd-cpu-mask"/>), DPDK worker
>> + threads will be unused.
>> </p>
>> <p>
>> - If not specified, the value will be determined by choosing the
>> lowest
>> - CPU core from initial cpu affinity list. Otherwise, the value
>> will be
>> - passed directly to the DPDK library.
>> + If this option is specified, OVS main/handler/revalidator threads
>> + will run on the selected DPDK main thread core.
>
> Should it be a bit clearer that they will all run on a single core, and this
> might not be desired?
> Maybe something along the lines of:
>
> If this option is specified, all OVS main, handler, and revalidator threads
> will be pinned to the selected DPDK main thread core. This means that
> potentially many threads will share a single CPU core, which may not be
> desirable for performance reasons.
>
Sounds good. Difficult to give performance advice because it depends on
system config/load etc, but in this case it's probably the right general
guidance and there is a qualifier ("which may not be".)
>> + </p>
>> + <p>
>> + If this option is not specified the value for DPDK initialization
>> + will be auto-determined and OVS main/revalidator/handler threads
>> will
>> + float on the OVS cpu affinity list.
>> </p>
>> </column>
>> --
>> 2.51.0
>>
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>
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