[ovs-dev] [PATCH] Documentation: Cleanup PMD information.

Tue Aug 10 12:09:28 UTC 2021

On 05/08/2021 09:32, Adrian Moreno wrote:
> 
> On 7/22/21 3:25 PM, Kevin Traynor wrote:
>> The 'Port/Rx Queue Assigment to PMD Threads' section has
>> expanded over time and now includes info about stats/commands,
>> manual pinning and different options for OVS assigning Rxqs to
>> PMDs.
>>
>> Split them into different sections with sub-headings and move
>> the two similar paragraphs about stats together.
>>
>> Rename 'Automatic assignment of Port/Rx Queue to PMD Threads'
>> section to 'PMD Automatic Load Balance'.
>>
>> A few other minor cleanups as I was reading.
>>
>> Signed-off-by: Kevin Traynor <ktraynor at redhat.com>
>> ---
>>  Documentation/topics/dpdk/pmd.rst | 101 ++++++++++++++++--------------
>>  1 file changed, 54 insertions(+), 47 deletions(-)
>>
>> diff --git a/Documentation/topics/dpdk/pmd.rst b/Documentation/topics/dpdk/pmd.rst
>> index 95fa7af12..45c24d100 100644
>> --- a/Documentation/topics/dpdk/pmd.rst
>> +++ b/Documentation/topics/dpdk/pmd.rst
>> @@ -75,8 +75,47 @@ for enabling things like multiqueue for :ref:`physical <dpdk-phy-multiqueue>`
>>  and :ref:`vhost-user <dpdk-vhost-user>` interfaces.
>>  
>> -To show port/Rx queue assignment::
>> +Rx queues will be assigned to PMD threads by OVS, or they can be  manually
>> +pinned to PMD threads by the user.
>> +
> 
> Nit: double space between "be" and "manually"

fixed.

> 
>> +To see the port/Rx queue assignment and current measured usage history of PMD
>> +core cycles for each Rx queue::
>>  
>>      $ ovs-appctl dpif-netdev/pmd-rxq-show
>>  
>> +.. note::
>> +
>> +   A history of one minute is recorded and shown for each Rx queue to allow for
>> +   traffic pattern spikes. Any changes in the Rx queue's PMD core cycles usage,
>> +   due to traffic pattern or reconfig changes, will take one minute to be fully
>> +   reflected in the stats.
>> +
>> +.. versionchanged:: 2.16.0
>> +
>> +   A ``overhead`` statistics is shown per PMD: it represents the number of
>> +   cycles inherently consumed by the OVS PMD processing loop.
>> +
>> +Rx queue to PMD assignment takes place whenever there are configuration changes
>> +or can be triggered by using::
>> +
>> +    $ ovs-appctl dpif-netdev/pmd-rxq-rebalance
>> +
>> +.. versionchanged:: 2.6.0
>> +
>> +   The ``pmd-rxq-show`` command was added in OVS 2.6.0.
>> +
>> +.. versionchanged:: 2.9.0
>> +
>> +   Utilization-based allocation of Rx queues to PMDs and the
>> +   ``pmd-rxq-rebalance`` command were added in OVS 2.9.0. Prior to this,
>> +   allocation was round-robin and processing cycles were not taken into
>> +   consideration.
>> +
>> +   In addition, the output of ``pmd-rxq-show`` was modified to include
>> +   Rx queue utilization of the PMD as a percentage. Prior to this, tracking of
>> +   stats was not available.
>> +
>> +
>> +Port/Rx Queue assignment to PMD threads by manual pinning
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>  Rx queues may be manually pinned to cores. This will change the default Rx
>>  queue assignment to PMD threads::
>> @@ -117,4 +156,6 @@ If using ``pmd-rxq-assign=group`` PMD threads with *pinned* Rxqs can be
>>     a *non-isolated* PMD, that will remain *non-isolated*.
>>  
>> +Automatic Port/Rx Queue assignment to PMD threads
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>  If ``pmd-rxq-affinity`` is not set for Rx queues, they will be assigned to PMDs
>>  (cores) automatically.
>> @@ -126,7 +167,9 @@ The algorithm used to automatically assign Rxqs to PMDs can be set by::
>>  By default, ``cycles`` assignment is used where the Rxqs will be ordered by
>>  their measured processing cycles, and then be evenly assigned in descending
>> -order to PMDs based on an up/down walk of the PMDs. For example, where there
>> -are five Rx queues and three cores - 3, 7, and 8 - available and the measured
>> -usage of core cycles per Rx queue over the last interval is seen to be:
>> +order to PMDs. The PMD that will be selected for a given Rxq will be the next
>> +one in alternating ascending/descending order based on core id. For example,
>> +where there are five Rx queues and three cores - 3, 7, and 8 - available and
>> +the measured usage of core cycles per Rx queue over the last interval is seen
>> +to be:
>>  
>>  - Queue #0: 30%
>> @@ -184,43 +227,6 @@ The Rx queues may be assigned to the cores in the following order::
>>      Core 8: P1Q0 |
>>  
>> -To see the current measured usage history of PMD core cycles for each Rx
>> -queue::
>> -
>> -    $ ovs-appctl dpif-netdev/pmd-rxq-show
>> -
>> -.. note::
>> -
>> -   A history of one minute is recorded and shown for each Rx queue to allow for
>> -   traffic pattern spikes. Any changes in the Rx queue's PMD core cycles usage,
>> -   due to traffic pattern or reconfig changes, will take one minute to be fully
>> -   reflected in the stats.
>> -
>> -.. versionchanged:: 2.16.0
>> -
>> -   A ``overhead`` statistics is shown per PMD: it represents the number of
>> -   cycles inherently consumed by the OVS PMD processing loop.
>> -
>> -Rx queue to PMD assignment takes place whenever there are configuration changes
>> -or can be triggered by using::
>> -
>> -    $ ovs-appctl dpif-netdev/pmd-rxq-rebalance
>> -
>> -.. versionchanged:: 2.6.0
>> -
>> -   The ``pmd-rxq-show`` command was added in OVS 2.6.0.
>> -
>> -.. versionchanged:: 2.9.0
>> -
>> -   Utilization-based allocation of Rx queues to PMDs and the
>> -   ``pmd-rxq-rebalance`` command were added in OVS 2.9.0. Prior to this,
>> -   allocation was round-robin and processing cycles were not taken into
>> -   consideration.
>> -
>> -   In addition, the output of ``pmd-rxq-show`` was modified to include
>> -   Rx queue utilization of the PMD as a percentage. Prior to this, tracking of
>> -   stats was not available.
>> -
>> -Automatic assignment of Port/Rx Queue to PMD Threads (experimental)
>> --------------------------------------------------------------------
>> +PMD Automatic Load Balance (experimental)
>> +-----------------------------------------
>>  
>>  Cycle or utilization based allocation of Rx queues to PMDs gives efficient
>> @@ -233,8 +239,9 @@ To address this automatic load balancing of PMDs can be set by::
>>      $ ovs-vsctl set open_vswitch . other_config:pmd-auto-lb="true"
>>  
>> -If pmd-auto-lb is set to true AND cycle based assignment is enabled then auto
>> -load balancing of PMDs is enabled provided there are 2 or more non-isolated
>> -PMDs and at least one of these PMDs is polling more than one RX queue. So,
>> -following conditions need to be met to have Auto Load balancing enabled:
>> +If pmd-auto-lb is set to true AND cycle or group based assignment is enabled
>> +then auto load balancing of PMDs is enabled provided there are 2 or more
>> +non-isolated PMDs and at least one of these PMDs is polling more than one RX
>> +queue. So, following conditions need to be met to have Auto Load balancing
>> +enabled:
>>  
>>  1. cycle based assignment of RX queues to PMD is enabled.
>>
> Should "group" assignment be added here as well? ^
> 

Yes, you are right. Actually re-reading that whole section, the
paragraph and the numbered conditions below it are just repeating the
same information. I removed the paragraph and fixed the first condition
as per comment.

> 
> Overall, this change makes the doc much easier to understand for someone new to
> the topic (such as myself).
> 
> Apart from the two small comments:
> Acked-by: Adrian Moreno <amorenoz at redhat.com>
> 
> Thanks
> 

Thanks for reviewing, Kevin.