[dpdk-dev] [PATCH] doc: flow rule removal on port stop
Gregory Etelson
getelson at nvidia.com
Wed Nov 18 10:06:23 CET 2020
> >> 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.
>
> Stop? Close? I agree and documentation should say so in a bit clear way.
I'll post updated document patch.
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