Re: [PATCH net-next] net/mlx5: Introduce SF direction

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 19 May 2023 11:30:44 -0700 Saeed Mahameed wrote:
> Whenever multiple Virtual Network functions (VNFs) are used by Service
> Function Chaining (SFC), each packet is passing through all the VNFs,
> and each VNF is performing hairpin in order to pass the packet to the
> next function in the chain.
> 
> In case one mlx5 NIC is servicing multiple VNFs of the SFC, mlx5 need
> user input in order to optimize this hairpin to a simple forward rule.
> 
> The optimization is performed by binding two PCI SFs to each VNF, as
> can be seen bellow:
> 
>              -----------          -----------
>              |   VNF1  |          |   VNF2  |
>              -----------          -----------
>                 |  |                 |  |
>        (Net) SF1|  |SF2     (Net) SF3|  |SF4
>                 |  |                 |  |
>              -------------------------------
>              | /   \________________/    \ |
>     uplink---|/                           \|----host
>              |                NIC(SFC)     |
>              |                             |
>              -------------------------------
> 
> Define SF1 and SF3 as SFs with network direction tell the driver to
> configure the E-switch in a way that the packet arriving from SF1 will
> do forward to SF2 instead of hairpin.
> 
> This marking is done via sfnum command line argument, where bit 16
> marks the SF as facing the Network, and bit 17 marks the SF as
> facing the Host.

What does it mean that an SF is "facing" the network?
Why can't the device automatically "optimize" the hairpin?
Or SF1 / SF2 will be uni-directional after this patch?
-- 
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