netdev - Re: net/mlx5e: bind() always returns EINVAL with XDP

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Message-ID: <20200618150347.ihtdvsfuurgfka7i@bsd-mbp.dhcp.thefacebook.com>
Date:   Thu, 18 Jun 2020 08:23:04 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Kal Cutter Conley <kal.conley@...tris.com>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        "brouer@...hat.com" <brouer@...hat.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        "magnus.karlsson@...el.com" <magnus.karlsson@...el.com>,
        "toke.hoiland-jorgensen@....se" <toke.hoiland-jorgensen@....se>,
        "xdp-newbies@...r.kernel.org" <xdp-newbies@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        "gospo@...adcom.com" <gospo@...adcom.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bjorn.topel@...el.com" <bjorn.topel@...el.com>
Subject: Re: net/mlx5e: bind() always returns EINVAL with XDP_ZEROCOPY

On Sun, Jun 14, 2020 at 10:55:30AM +0200, Kal Cutter Conley wrote:
> Hi Saeed,
> Thanks for explaining the reasoning behind the special mlx5 queue
> numbering with XDP zerocopy.
> 
> We have a process using AF_XDP that also shares the network interface
> with other processes on the system. ethtool rx flow classification
> rules are used to route the traffic to the appropriate XSK queue
> N..(2N-1). The issue is these queues are only valid as long they are
> active (as far as I can tell). This means if my AF_XDP process dies
> other processes no longer receive ingress traffic routed over queues
> N..(2N-1) even though my XDP program is still loaded and would happily
> always return XDP_PASS. Other drivers do not have this usability issue
> because they use queues that are always valid. Is there a simple
> workaround for this issue? It seems to me queues N..(2N-1) should
> simply map to 0..(N-1) when they are not active?

If your XDP program returns XDP_PASS, the packet should be delivered to
the xsk socket.  If the application isn't running, where would it go?

I do agree that the usability of this can be improved.  What if the flow
rules are inserted and removed along with queue creatioin/destruction?
-- 
Jonathan