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

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Date:   Sat, 20 Jun 2020 11:42:02 -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>,
        "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 Sat, Jun 20, 2020 at 12:42:36PM +0200, Kal Cutter Conley wrote:
> On Thu, Jun 18, 2020 at 5:23 PM Jonathan Lemon <jonathan.lemon@...il.com> wrote:
> >
> > 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?
> 
> I think I misunderstood your suggestion here. Do you mean the rules
> should be inserted / removed on the hardware level but still show in
> ethtool even if they are not active in the hardware? In this case the
> rules always occupy a "location" but just never apply if the
> respective queues are not "enabled". I think this would be the best
> possible solution.

No, that wasn't what I was suggesting.  I would think that having
ethtool return something that isn't true woulld be really confusing -
either the rules are enabled and active, or they should not be there.

I was thinking more along the lines of having the flow rules inserted
and removed when the queue is created/destroyed, so the steering rule is
a property of the queue itself rather than maintained externally through
ethtool.
-- 
Jonathan