Re: [dpdk-dev] [PATCH v2] doc: flow rule removal on port stop

[Thomas Monjalon <thomas@monjalon.net>]

Andrew, any comment on this v2?
(disclosure: I did not read it)


18/11/2020 17:15, Gregory Etelson:
> There is a discrepancy between RTE ETHDEV API and flow rules guide
> regarding flow rules maintenance after port stop.  RTE ETHDEV API in
> librte_ethdev.h declares that flow rules will not be stored in PMD
> after port stop:
>  >>>>> Quite start
>  Please note that some configuration is not stored between calls to
>  rte_eth_dev_stop()/rte_eth_dev_start(). The following configuration
>  will be retained:
> 
>  - MTU
>  - flow control settings
>  - receive mode configuration (promiscuous mode, all-multicast mode,
>    hardware checksum mode, RSS/VMDQ settings etc.)
>  - VLAN filtering configuration
>  - default MAC address
>  - MAC addresses supplied to MAC address array
>  - flow director filtering mode (but not filtering rules)
>  - NIC queue statistics mappings
>  <<<< Quote end
> 
> PMD cannot always correctly restore flow rules after port stop / port
> start because application may alter port configuration after port stop
> without PMD knowledge about undergoing changes.  Consider the
> following scenario:
> application configures 2 queues 0 and 1 and creates a flow rule with
> 'queue index 1' action. After that application stops the port and
> removes queue 1.
> Although PMD can implement flow rule shadow copy to be used for
> restore after port start, attempt to restore flow rule from shadow
> will fail in example above and PMD could not notify application about
> that failure.  As the result, flow rules map in HW will differ from
> what application expects.  In addition, flow rules shadow copy used
> for port start restore consumes considerable amount of system memory,
> especially in systems with millions of flow rules.
> 
> Signed-off-by: Gregory Etelson <getelson@nvidia.com>
> Acked-by: Ori Kam <orika@nvidia.com>
> ---
>  doc/guides/prog_guide/rte_flow.rst | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/doc/guides/prog_guide/rte_flow.rst b/doc/guides/prog_guide/rte_flow.rst
> index ea203e0ca4..4cff9332fa 100644
> --- a/doc/guides/prog_guide/rte_flow.rst
> +++ b/doc/guides/prog_guide/rte_flow.rst
> @@ -3229,10 +3229,12 @@ Caveats
>    temporarily replacing the burst function pointers), an appropriate error
>    code must be returned (``EBUSY``).
>  
> -- PMDs, not applications, are responsible for maintaining flow rules
> -  configuration when stopping and restarting a port or performing other
> -  actions which may affect them. They can only be destroyed explicitly by
> -  applications.
> +- Applications, not PMDs, are responsible for maintaining flow rules
> +  configuration when closing, stopping or restarting a port or performing other
> +  actions which may affect them.
> +  Applications must assume that after port close, stop or restart all flows
> +  related to that port are not valid, hardware rules are destroyed and relevant
> +  PMD resources are released.
>  
>  For devices exposing multiple ports sharing global settings affected by flow
>  rules:
>