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

[Shahaf Shuler]

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 at 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).

> 
> --
> Adrien Mazarguil
> 6WIND