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

["Medvedkin, Vladimir" <vladimir.medvedkin@intel.com>]

Hi Stephen,

Thanks for the feedback,

On 08/04/2021 18:56, Stephen Hemminger wrote:
> 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.

Agree, I think it would be great to have a simple NAT implementation in 
examples. We've discussed this and will probably add in next releases.

> 

-- 
Regards,
Vladimir