linux-kernel - Re: [PATCH net-next 2/2] virtio-net: simplify XDP handling in small buffer

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Message-ID: <20180301101553.55c4c6bd@redhat.com>
Date:   Thu, 1 Mar 2018 10:15:53 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        john.fastabend@...il.com, brouer@...hat.com
Subject: Re: [PATCH net-next 2/2] virtio-net: simplify XDP handling in small
 buffer

On Thu, 1 Mar 2018 16:49:24 +0800
Jason Wang <jasowang@...hat.com> wrote:

> > 2. This can easily cause out-of-order packets.  
> 
> I may miss something, but it looks to me packets were still delivered
> in order? Or you mean the packets that was dropped by cpumap?

No. Packets can now travel two code paths to the egress device. (1) XDP
native via ndp_xdp_xmit via direct delivery into a lockfree/dedicated
TX queue, (2) via normal network stack which can involve being queue in
a qdisc.  Do you see the possibility of the reorder now?

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