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

Thu Aug 5 08:32:26 UTC 2021

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"

> +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? ^

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
-- 
Adrián Moreno