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

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Wednesday, July 8, 2020 5:58 PM
> To: Ye, Xiaolong <xiaolong.ye@intel.com>; Xing, Beilei
> <beilei.xing@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>
> Cc: dev@dpdk.org; Guo, Jia <jia.guo@intel.com>; Guo, Junfeng
> <junfeng.guo@intel.com>; Su, Simei <simei.su@intel.com>; Yigit, Ferruh
> <ferruh.yigit@intel.com>; arybchenko@solarflare.com;
> viacheslavo@mellanox.com; jerinj@marvell.com;
> ajit.khaparde@broadcom.com; orika@mellanox.com
> Subject: Re: [dpdk-dev] [PATCH v2 1/3] ethdev: add new RSS types for IPv6
> prefix
> 
> 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.
> > > Do we want to continue with the RTE_ prefix missing?
> > > Can't we add the prefix for the new values?
> 
> I think you misunderstood this question. I am asking to change the name
> ETH_RSS_L3_PRE32 to RTE_ETH_RSS_L3_PRE32

OK, we are going change all the ETH_RSS_xxx to RTE_ETH_RSS_xxx, or just the new values?
the first option looks make sense to me.
 
> 
> > 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
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.
> 
>