Re: [dpdk-dev] [PATCH 1/2] ethdev: add symmetric toeplitz hash support

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

> -----Original Message-----
> From: Su, Simei
> Sent: Monday, September 30, 2019 2:34 PM
> To: Andrew Rybchenko <arybchenko@solarflare.com>; Shahaf Shuler
> <shahafs@mellanox.com>; Adrien Mazarguil <adrien.mazarguil@6wind.com>
> Cc: Zhang, Qi Z <qi.z.zhang@intel.com>; Wu, Jingjing <jingjing.wu@intel.com>;
> dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH 1/2] ethdev: add symmetric toeplitz hash
> support
> 
> Hi, Andrew
> 
> > -----Original Message-----
> > From: Andrew Rybchenko [mailto:arybchenko@solarflare.com]
> > Sent: Monday, September 30, 2019 2:15 PM
> > To: Su, Simei <simei.su@intel.com>; Shahaf Shuler
> > <shahafs@mellanox.com>; Adrien Mazarguil <adrien.mazarguil@6wind.com>
> > Cc: Zhang, Qi Z <qi.z.zhang@intel.com>; Wu, Jingjing
> > <jingjing.wu@intel.com>; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add symmetric toeplitz
> > hash support
> >
> > Hi Simei,
> >
> > On 9/30/19 6:12 AM, Su, Simei wrote:
> > > Hi, Andrew
> > >
> > >> -----Original Message-----
> > >> From: Andrew Rybchenko [mailto:arybchenko@solarflare.com]
> > >> Sent: Sunday, September 29, 2019 7:51 PM
> > >> To: Shahaf Shuler <shahafs@mellanox.com>; Adrien Mazarguil
> > >> <adrien.mazarguil@6wind.com>
> > >> Cc: Su, Simei <simei.su@intel.com>; Zhang, Qi Z
> > >> <qi.z.zhang@intel.com>; Wu, Jingjing <jingjing.wu@intel.com>;
> > >> dev@dpdk.org
> > >> Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add symmetric toeplitz
> > >> hash support
> > >>
> > >> On 7/31/19 4:43 PM, Shahaf Shuler wrote:
> > >>> Wednesday, July 31, 2019 3:31 PM, Adrien Mazarguil:
> > >>>> Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add symmetric
> > >>>> toeplitz hash support
> > >>>>
> > >>>> On Wed, Jul 31, 2019 at 03:08:19PM +0300, Andrew Rybchenko wrote:
> > >>>>> On 7/25/19 7:57 AM, simei wrote:
> > >>>>>> From: Simei Su <simei.su@intel.com>
> > >>>>>>
> > >>>>>> Currently, there are DEFAULT,TOEPLITZ and SIMPLE_XOR hash
> funtion.
> > >>>>>> To support symmetric hash by rte_flow RSS action, this patch
> > >>>>>> adds new hash function "Symmetric Toeplitz" which is supported
> > >>>>>> by some
> > >>>> hardware.
> > >>>>> Isn't it a question of key to achieve symmetry?
> > >>>>> I.e. hash algorithm (function) is still the same - Toeplitz, but
> > >>>>> hash key makes the result symmetric (i.e. equal for flows in
> > >>>>> both directions - swap transport ports and IPv4/6 addresses).
> > >>>> This is only an option when src/dst are known in advance.
> > >>>>
> > >>>> When doing RSS, HW implementations (such as Mellanox's) implement
> > >>>> a modified Toeplitz XOR'ing src with dst resulting in the same
> > >>>> hash both ways regardless of the key.
> > >>> Just to stand correct it was a bug on Mellanox kernel driver that
> > >>> was fixed. Now
> > >> the RSS is spec complaint (non-symmetric).
> > >>> Andrew is correct one can have a special key that will make the
> > >>> RSS symmetric,
> > >> however it is good to have this option for the user to explicitly
> > >> request symmetric function (w/o any restriction on the key).
> > >>
> > >> I think we need a definition what is behind SYMMETRIC_TOEPLITZ here.
> > >> If I'd like to test it and check, I need to know an algorithm in
> > >> order to know what to expect.
> > >> Also it is important to make it the same for all NIC vendors: what
> > >> should algorithm be in order to say that it is symmetric Toeplitz?
> > > The symmetric toeplitz is: src, dst will be replaced by xor(src, dst).
> > > It is expected to get the same hash value when swapping src/dst ip or port.
> >
> > Are both replaced by XOR or just one is replaced by XOR and another
> > one removed from Toeplitz input? If later, how does it coexist with src/dst
> only flags?
> >
> > Anyway, please, add it to the patch in Doxygen comments.
> >
>   In our case, src and dst are both replaced by XOR. For example, src ip and
> dst ip or src port and dst port are swapped, the hash value is the same.
>   SRC/DST only flags is another thing, it covers input set change.

For the case with dst / src only, src or dst address will XOR with zero pair, so it result same value as simple Toeplitz

> 
> Br
> Simei
> 
> > Thanks,
> > Andrew.