RE: [PATCH v4 1/2] ethdev: add random item support

[Michael Baum <michaelba@nvidia.com>]

On 12/14/2023 5:56 PM, Ferruh Yigit wrote:
> 
> On 12/14/2023 1:43 PM, Michael Baum wrote:
> >
> > On 12/14/2023 2:18 PM, Ferruh Yigit wrote:
> >>
> >> On 12/14/2023 10:58 AM, Michael Baum wrote:
> >>> Add support for a new item type "RTE_FLOW_ITEM_TYPE_RANDOM".
> >>> This item enables to match on some random value as a part of flow rule.
> >>>
> >
> > ...
> >
> >>>
> >>> +Item: ``RANDOM``
> >>> +^^^^^^^^^^^^^^^^
> >>> +
> >>> +Matches a random value.
> >>> +
> >>> +A random unsigned integer (at most 32-bit) is generated for each
> >>> +packet during flow rule processing, by either HW, SW or some external
> source.
> >>> +Application can match on either exact value or range of values.
> >>> +This value is not based on the packet data/headers.
> >>> +Application shouldn't assume that this value is kept during the
> >>> +lifetime of the packet.
> >>> +
> >>> +- ``value``: Specific value to match.
> >>> +
> >>
> >>
> >> Hi Michael,
> >>
> >> What is the usecase for the 'random' flow item?
> > I can think about 2 different use cases:
> > 1. Sampling - when application wants to sample certain percentage of the flow,
> it can match random value for getting it.
> > 2. Distribution - when application wants to distribute the traffic between
> ports/queues, it can match all random value range with send to port/queue
> actions.
> >
> >>
> >> Is it to match some kind of metadata generated by HW?
> > It can be generated by either HW, SW or some external source.
> > Each PMD supporting random item responds to have a generator for that.
> >
> >> Or is it a way to sampling traffic?
> > It can be both. The PMD can use random value generated by HW while user
> match on it for sampling traffic.
> >
> >>
> >> And how random 'random' item is, is it configured/set in HW or random per
> packet?
> > From API perspective, it is pure random not packet oriented. Same packet can
> get different values during the pipeline.
> > I mentioned it in documentation:
> > "This value is not based on the packet data/headers.
> > Application shouldn't assume that this value is kept during the lifetime of the
> packet."
> >
> 
> Thanks Michael, for clarification.
> 
> I was thinking if this can be used together with external (to DPDK) flow steering
> configuration.
> Like external tool can set values to match for specific pattern, tcp --> 100 udp -->
> 200 Later these values can be used by DPDK application and this filtering item.
> 
> Can you please confirm this is not the "use case"/intention, if so we may need to
> rename the rte flow item.

Hi,  this is not the use-case.
> 
> Also there will be driver implementation in this release, right?

Yes, series-30558 ("net/mlx5: add random item support")
https://patchwork.dpdk.org/project/dpdk/cover/20231214151248.1654878-1-michaelba@nvidia.com/