Re: [dpdk-dev] [PATCH v2 1/3] ethdev: add new RSS types for IPv6 prefix

[Thomas Monjalon <thomas@monjalon.net>]

08/07/2020 14:05, Zhang, Qi Z:
> From: Thomas Monjalon <thomas@monjalon.net>
> > 08/07/2020 13:10, Zhang, Qi Z:
> > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > 08/07/2020 11:45, Zhang, Qi Z:
> > > > > On 2020/7/7 19:06, Thomas Monjalon wrote:
> > > > > > 16/06/2020 10:16, Junfeng Guo:
> > > > > >> This patch defines new RSS offload types for IPv6 prefix with
> > > > > >> 32, 48,
> > > > > >> 64 bits of both SRC and DST IPv6 address.
> > > > > >>
> > > > > >> Signed-off-by: Junfeng Guo <junfeng.guo@intel.com>
> > > > > >> ---
> > > > > >>   lib/librte_ethdev/rte_ethdev.h | 51
> > > > ++++++++++++++++++++++++++++++++++
> > > > > >>   1 file changed, 51 insertions(+)
> > > > > >>
> > > > > >> diff --git a/lib/librte_ethdev/rte_ethdev.h
> > > > > >> b/lib/librte_ethdev/rte_ethdev.h index 631b146bd..5a7ba36d8
> > > > > >> 100644
> > > > > >> --- a/lib/librte_ethdev/rte_ethdev.h
> > > > > >> +++ b/lib/librte_ethdev/rte_ethdev.h
> > > > > >> @@ -538,6 +538,9 @@ struct rte_eth_rss_conf {
> > > > > >>   #define ETH_RSS_L4_DST_ONLY        (1ULL << 60)
> > > > > >>   #define ETH_RSS_L2_SRC_ONLY        (1ULL << 59)
> > > > > >>   #define ETH_RSS_L2_DST_ONLY        (1ULL << 58)
> > > > > >> +#define ETH_RSS_L3_PRE32           (1ULL << 57)
> > > > > >> +#define ETH_RSS_L3_PRE48           (1ULL << 56)
> > > > > >> +#define ETH_RSS_L3_PRE64           (1ULL << 55)
> > > > > >
> > > > > > PRE32, 48 and 64 are not obvious.
> > > > > > Why is it needed?
> > > > >
> > > > > there is typical usage for NAT64, which use 32 bit prefix for IPv6
> > > > > addresses, in this case flows over IPv4 and IPv6 will result in
> > > > > the same hash value, as well as 48, 64, which also have some
> > > > > corresponding use cases,
> > > > > > At least, please add comments for the values of this API.
> > > > >
> > > > > sure, we will add more comments.
[...]
> > > > > 32, 48, 64 are typical usage, and consider suffix pair we may add
> > > > > later, it will cost 6 bits so far we still have 27 bit left,  so
> > > > > it looks like will not be a problem in following couple releases.
> > > >
> > > > Having some space left is not a reason to waste it :) If I
> > > > understand well, there is no standard for this API.
> > > > You are assigning some bits to some usage.
> > > > I don't find it generic and flexible enough.
> > >
> > > Actually IPv6 address prefix is in spec, please check below RFC.
> > > https://tools.ietf.org/html/rfc6052#page-5
> > 
> > Quoting the RFC:
> > "
> >    the prefix shall be either the "Well-Known Prefix"
> >    or a "Network-Specific Prefix" unique to the organization
> >    deploying the address translators.
> >    The prefixes can only have one of the following lengths:
> >    32, 40, 48, 56, 64, or 96.
> >    (The Well-Known Prefix is 96 bits long, and can only be used
> >    in the last form of the table.)
> > "
> > 
> > So 40 and 56 are missing.
> 
> Yes, like to add and lets accelerate the progress to abandon the old APIs :)

Please could list which part of the existing API you would like
to deprecate in future?


> > > So probably we are not wasting bits here, since this is a typical
> > > usage that DPDK can provide.
> > > Of cause more description is needed in the code here.
> > >
> > > > If you want to limit the size of the match, we should have a generic
> > > > syntax to choose how many bits of the IPv6 address are taken into
> > > > account for RSS. Or maybe an IPv6 mask.
> > >
> > > Yes, I believe at some moment, a more generic solution is mandatory,
> > > And I think that will not work if we stick on the 64 bits, new API
> > > need to be introduced and old one should be abandoned
> > >
> > > >
> > > > > but anyway use 64 bits to represent RSS inputset can't meet the
> > > > > coming complex RSS usage, we may need to figure out some new APIs
> > > > > and
> > > > abandon
> > > > > the old one.
> > > > > A stacked protocol layer with bit field selector in each layer is
> > > > > under consideration, hope we can contribute some RFC at some
> > moment.
> > > > > also feel free let us know your thought.
> > > >
> > > > My thought is to discuss how to fit this need in future and avoid
> > > > adding few bits of temporary workaround.
> > > > API definition is serious and we must avoid temporary half solutions.