netdev - Re: [PATCH net-next 7/8] net/mlx5e: XDP TX forwarding support

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Message-ID: <20160920180609.148874b5@redhat.com>
Date:   Tue, 20 Sep 2016 18:06:09 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Tom Herbert <tom@...bertland.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tariq Toukan <ttoukan.linux@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Rana Shahout <ranas@...lanox.com>, brouer@...hat.com
Subject: Re: [PATCH net-next 7/8] net/mlx5e: XDP TX forwarding support

On Tue, 20 Sep 2016 08:58:30 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

> On Tue, 2016-09-20 at 08:51 -0700, Tom Herbert wrote:
> > On Tue, Sep 20, 2016 at 8:40 AM, Alexei Starovoitov
> > <alexei.starovoitov@...il.com> wrote:  
> > > On Tue, Sep 20, 2016 at 03:53:10PM +0300, Tariq Toukan wrote:  
> > >> >>>+  case XDP_ABORTED:  
> > >> >>It is not clearly defined, but I believe XDP_ABORTED should also result
> > >> >>in a warning (calling bpf_warn_invalid_xdp_action(act)).  
> > >> I'll add this.  
> > >
> > > Certainly NOT.
> > > XDP_ABORTED is an exception case when program does divide by zero.
> > > It should NOT do bpf_warn. It must drop the packet.
> > > We discussed it several months ago.
> > > See mlx4/en_rx.c for canonical implementation.
> > >  
> > It should at least bump a counter so that the user knows that aborts
> > are happening.  

I agree.

> Same for XDP_TX if/when packet is dropped because output ring is full.

For the XDP_TX case a counter is already incremented[1] but it is a
local ring counter (ring->tx_dropped++).

Do you think we should maintain separate counters for XDP? (to have a
more consistent interface across drivers...)


[1] https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/mellanox/mlx4/en_tx.c#L1181

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer