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

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 11/17/20 10:18 PM, Gregory Etelson wrote:
> 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 | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/guides/prog_guide/rte_flow.rst b/doc/guides/prog_guide/rte_flow.rst
> index 944e8242d6..dfe5a40f8e 100644
> --- a/doc/guides/prog_guide/rte_flow.rst
> +++ b/doc/guides/prog_guide/rte_flow.rst
> @@ -3055,10 +3055,9 @@ Caveats
>     temporarily replacing the burst function pointers), an appropriate error
>     code must be returned (``EBUSY``).
>   
> -- PMDs, not applications, are responsible for maintaining flow rules
> +- Applications, not PMDs, 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.
> +  actions which may affect them.
>   
>   For devices exposing multiple ports sharing global settings affected by flow
>   rules:
> 

Re-reading it, it still looks vague. What happens on:
  - port stop without removal of flow rule before
  - port close without removal of flow rules before
  - port reset (which could be stop/start, e.g. to recover from error 
condition)