[dpdk-dev] [PATCH v2] doc: update RSS action with best effort

[Ori Kam]

Hi Andrew,

> -----Original Message-----
> From: Andrew Rybchenko <arybchenko at solarflare.com>
> On 8/5/20 5:08 PM, Ori Kam wrote:
> > Hi Andrew,
> >
> >> -----Original Message-----
> >> From: Andrew Rybchenko <arybchenko at solarflare.com>
> >>
> >> On 8/4/20 11:13 AM, Ori Kam wrote:
> >>> Using the rte_flow action RSS types field,
> >>> may result in undefined outcome.
> >>>
> >>> For example selecting both UDP and TCP,
> >>> selecting TCP RSS type but the pattern is targeting UDP traffic.
> >>> another option is that the PMD doesn't support all requested types.
> >>>
> >>> Until now, it wasn't clear what will happen in such cases.
> >>> This commit clarify this issue by stating that the PMD
> >>> will work in the best-effort mode.
> >>>
> >>> Signed-off-by: Ori Kam <orika at mellanox.com>
> >>> ---
> >>> v2:
> >>>  * Based on ML, update that using only unsupported hash type
> >>>    may cause the flow to be rejected by PMD.
> >>> ---
> >>>  doc/guides/prog_guide/rte_flow.rst | 11 +++++++++++
> >>>  1 file changed, 11 insertions(+)
> >>>
> >>> diff --git a/doc/guides/prog_guide/rte_flow.rst
> >> b/doc/guides/prog_guide/rte_flow.rst
> >>> index 3e5cd1e..d730b66 100644
> >>> --- a/doc/guides/prog_guide/rte_flow.rst
> >>> +++ b/doc/guides/prog_guide/rte_flow.rst
> >>> @@ -1735,6 +1735,17 @@ unspecified "best-effort" settings from the
> >> underlying PMD, which depending
> >>>  on the flow rule, may result in anything ranging from empty (single queue)
> >>>  to all-inclusive RSS.
> >>>
> >>> +Best effort will be used, in case there is a conflict inside the rule.
> >>> +The conflict can be the result of:
> >>> +
> >>> +- Conflicting RSS types, for example setting both UDP and TCP.
> >>
> >> Thinking more about it, I see no conflict at all. It is common
> >> to specify both TCP and UDP in hash function if user wants to
> >> take TCP ports for TCP packets and UDP ports for UDP into
> >> account.
> >>
> > I fully agree with you that it is common to use both UDP and TCP and
> > expect it to work based on the traffic. this is the point of this patch.
> > To clarify that this is valid input and the PMD will work in best effort mode.
> 
> Just don't name it "Conflicting RSS types", may be
> "Non-applicable RSS types", but it collapses two
> bullets into one.

Will rephrase.
> 
> >
> >>> +
> >>> +- Conflicting between RSS types and the requested pattern to match,
> >>> +  for example matching on UDP and hashing RSS on TCP.
> >>
> >> I'd not name it a conflict either. It is just common rule when
> >> applicable fields are used only.
> >>
> > Just like my comment from above.
> >
> >>> +
> >>> +If requested RSS hash type is not supported,
> >>> +and no supported hash type is requested then the PMD may reject the
> flow.
> >>> +
> >>
> >> I disagree with such description. If requested RSS hash type is
> >> not supported (not present in dev_info.flow_type_rss_offloads),
> >> it must be rejected and error returned.
> >> If requested RSS hash type is not supported for a packet
> >> matching the rule, but supported in general (present in
> >> dev_info.flow_type_rss_offloads), part of RSS hash type
> >> specification may be ignored and only applicable bits are used.
> >> If result is empty, PMD may reject the flow rule.
> >>
> > The flow should be rejected even if it is used with some type that is
> supported?
> 
> Yes, if user ask for something what is not supported at all,
> it is a problem and user should be notified. May be it is
> too restrictive, but I'd prefer this way.
> User has all required information in dev_info and can
> remove unsupported hash types from request. IMHO, it
> should enforce user check the result to be not empty and
> handle it properly.
> 
Will update the doc.
> >
> >
> >>>  Note: RSS hash result is stored in the ``hash.rss`` mbuf field which
> >>>  overlaps ``hash.fdir.lo``. Since `Action: MARK`_ sets the ``hash.fdir.hi``
> >>>  field only, both can be requested simultaneously.
> >>>
> >