[dpdk-dev] Possible bug in mlx5_tx_burst_mpw?

Adrien Mazarguil adrien.mazarguil at 6wind.com
Wed Sep 14 16:30:34 CEST 2016

Hi Luke,

On Wed, Sep 14, 2016 at 03:24:07PM +0200, Luke Gorrie wrote:
> Howdy,
> Just noticed a line of code that struck me as odd and so I am writing just
> in case it is a bug:
> http://dpdk.org/browse/dpdk/tree/drivers/net/mlx5/mlx5_rxtx.c#n1014
> Specifically the check "(mpw.length != length)" in mlx_tx_burst_mpw() looks
> like a descriptor-format optimization for the special case where
> consecutive packets on the wire are exactly the same size. This would
> strike me as peculiar.
> Just wanted to check, is that interpretation correct and if so then is this
> intentional?

Your interpretation is correct (this is intentional and not a bug).

In the event successive packets share a few properties (length, number of
segments, offload flags), these can be factored out as an optimization to
lower the amount of traffic on the PCI bus. This feature is currently
supported by the ConnectX-4 Lx family of adapters.

Adrien Mazarguil

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