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

[Gregory Etelson]

Hello Andrew,

> 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 at nvidia.com>
> > Acked-by: Ori Kam <orika at 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)

PMD should remove all flows related to hardware resource that was invalidated.