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

[Gregory Etelson <getelson@nvidia.com>]

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:
-- 
2.25.1