Re: [dpdk-dev] [PATCH v2 0/3] Predictable RSS feature

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue,  6 Apr 2021 20:50:40 +0100
Vladimir Medvedkin <vladimir.medvedkin@intel.com> wrote:

> This patch series introduces predictable RSS feature.
> It is based on the idea of searching for partial hash collisions
> within Toeplitz hash.
> 
> The Toeplitz hash function is a homomorphism between (G, ^) and (H, ^),
> where (G, ^) - is a group of tuples and (H, ^) is a group of hashes
> with respect to XOR operation. So tuples and hashes could be treated as
> n-dimension and 32-dimension vector spaces over GF(2).
> So, f(x ^ y) == f(x) ^ f(y)
> where f - is the toeplitz hash function and x, y are tuples.
> 
> The ability to predict partial collisions allows user to compute
> input hash value with desired LSB values.
> Usually number of LSB's are defined by the size of RSS Redirection Table.
> 
> There could be number of use cases, for example:
> 1) NAT. Using this library it is possible to select a new port number
> on a translation in the way that rss hash for original tuple will have
> the same LSB's as rss hash for reverse tuple.
> 2) IPSec/MPLS/Vxlan. It is possible to choose tunnel id to be pinned to
> a desired queue.
> 3) TCP stack. It is possible to choose a source port number for outgoing
> connections in the way that received replies will be assigned to
> desired queue.
> 4) RSS hash key generation. Hash key initialization with random values
> does not guarantee an uniform distribution amongst queues. This library
> uses mathematically proved algorithm to complete the rss hash key to
> provide the best distribution.
> 
> v2:
> - added extra API rte_thash_adjust_tuple()
> - added extra tests for rte_thash_adjust_tuple()
> - added extra fields to rte_thash_subtuple_helper struct
> - fixed typos 
> 
> Vladimir Medvedkin (3):
>   hash: add predictable RSS API
>   hash: add predictable RSS implementation
>   test/hash: add additional thash tests
> 
>  app/test/test_thash.c       | 468 +++++++++++++++++++++++++++++++-
>  lib/librte_hash/meson.build |   3 +-
>  lib/librte_hash/rte_thash.c | 637 ++++++++++++++++++++++++++++++++++++++++++++
>  lib/librte_hash/rte_thash.h | 180 +++++++++++++
>  lib/librte_hash/version.map |   8 +
>  5 files changed, 1289 insertions(+), 7 deletions(-)
>  create mode 100644 lib/librte_hash/rte_thash.c
> 

It would be good to show how this could be used in an application.
Maybe yet another variant/flag to l3fwd example.