Re: [dpdk-dev] Q on IXGBE and I40E vector Tx processing

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Ravi,

> 
> Hi,
> 
> The reason I am asking I because I have tried different combinations of
> scalar and vector Tx and Rx processing for both IXGBE and I40E with
> following results
> 
> 1. Vector Rx and Vector Tx gives best performance but can only support
> packet size of less than or equal to 2048 bytes
> 
> 2. Scalar Rx and Scalar Tx works for all packet size but with degraded
> performance
> 
> 3. Vector Rx and Scalar Tx (with certain PMD configuration) works fine
> (performance doesn't meet '1') but it has an inherent bug for packet size
> 8192 bytes as PMD stops packet processing
> 
> From the code I see both IXGBE and I40E can support scattered vector Rx, I
> am curious to know any obvious reasons scattered vector Tx support is left
> out and does it make sense to implement it?
> 
> If it makes sense to implement scattered vector Tx and Intel team hasn't
> worked on it I would like to make an attempt at it so kindly let me know.
>

Yes, right now there is a tradeoff - simple TX functions (both vector and scalar) are much
faster than full-featured TX function, but don't support any TX offloads or multi-segs.
If you'd like to provide a patch that would add  some TX offloads to the simple path
without any performance degradation or either a patch that would improve performance
of full-featured TX function - I am pretty sure such patches would be welcomed. 
Konstantin