netdev - Re: [PATCH mlx5-next 11/16] net/mlx5: Add VDPA priority to NIC RX namespace

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Date:   Tue, 24 Nov 2020 14:02:10 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Saeed Mahameed <saeedm@...dia.com>, Eli Cohen <elic@...dia.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        <netdev@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        Eli Cohen <eli@...lanox.com>, Mark Bloch <mbloch@...dia.com>,
        Maor Gottlieb <maorg@...dia.com>
Subject: Re: [PATCH mlx5-next 11/16] net/mlx5: Add VDPA priority to NIC RX
 namespace

On Tue, Nov 24, 2020 at 09:12:19AM -0800, Jakub Kicinski wrote:
> On Sun, 22 Nov 2020 08:41:58 +0200 Eli Cohen wrote:
> > On Sat, Nov 21, 2020 at 04:01:55PM -0800, Jakub Kicinski wrote:
> > > On Fri, 20 Nov 2020 15:03:34 -0800 Saeed Mahameed wrote:  
> > > > From: Eli Cohen <eli@...lanox.com>
> > > > 
> > > > Add a new namespace type to the NIC RX root namespace to allow for
> > > > inserting VDPA rules before regular NIC but after bypass, thus allowing
> > > > DPDK to have precedence in packet processing.  
> > > 
> > > How does DPDK and VDPA relate in this context?  
> > 
> > mlx5 steering is hierarchical and defines precedence amongst namespaces.
> > Up till now, the VDPA implementation would insert a rule into the
> > MLX5_FLOW_NAMESPACE_BYPASS hierarchy which is used by DPDK thus taking
> > all the incoming traffic.
> > 
> > The MLX5_FLOW_NAMESPACE_VDPA hirerachy comes after
> > MLX5_FLOW_NAMESPACE_BYPASS.
> 
> Our policy was no DPDK driver bifurcation. There's no asterisk saying
> "unless you pretend you need flow filters for RDMA, get them upstream
> and then drop the act".

Huh?

mlx5 DPDK is an *RDMA* userspace application. It links to
libibverbs. It runs on the RDMA stack. It uses RDMA flow filtering and
RDMA raw ethernet QPs. It has been like this for years, it is not some
"act".

It is long standing uABI that accelerators like RDMA/etc get to take
the traffic before netdev. This cannot be reverted. I don't really
understand what you are expecting here?

Jason