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

[Wang, Yipeng1]

> -----Original Message-----
> From: Medvedkin, Vladimir <vladimir.medvedkin at intel.com>
> Sent: Tuesday, April 6, 2021 12:51 PM
> To: dev at dpdk.org
> Cc: Ananyev, Konstantin <konstantin.ananyev at intel.com>; Chilikin, Andrey
> <andrey.chilikin at intel.com>; Kinsella, Ray <ray.kinsella at intel.com>; Wang,
> Yipeng1 <yipeng1.wang at intel.com>; Gobriel, Sameh
> <sameh.gobriel at intel.com>; Richardson, Bruce
> <bruce.richardson at intel.com>
> Subject: [PATCH v2 0/3] Predictable RSS feature
> 
> 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
> 
> --
> 2.7.4

[Wang, Yipeng] 
Hi, Vladimir, thanks for the patch!
I haven't fully understood every bit of the algorithm yet, 
but I did see issues that this patch could potentially solve.
My understanding is that there are some restrictions for the current implementation,
for example, it only supports port(16-bit) manipulation, but not multiple fields or IP. 
Still, I think it should be good for the use cases you listed. I would love to hear
more feedbacks from people who are more familiar with doing NAT in production systems.

For me, besides the comments I sent earlier,
good documentation and references are needed with clear usage examples, as others pointed out already.

Also, the current API design seems a bit cumbersome.
To use the library, one needs:
Init_ctx
Add_helper.
Get_helper
Get_complement
Then in a loop:
Adjust_tuples
Then XOR with the current tuple

I wonder if an alternative all-in-one API could be designed for simpler use cases.

Thanks!