netdev - Re: [PATCH net-next] virtio-net: switch to use build

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Date:   Wed, 22 Feb 2017 05:06:34 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] virtio-net: switch to use build_skb() for small
 buffer

On Wed, Feb 22, 2017 at 10:58:08AM +0800, Jason Wang wrote:
> 
> 
> On 2017年02月21日 22:37, Michael S. Tsirkin wrote:
> > On Tue, Feb 21, 2017 at 04:46:28PM +0800, Jason Wang wrote:
> > > This patch switch to use build_skb() for small buffer which can have
> > > better performance for both TCP and XDP (since we can work at page
> > > before skb creation). It also remove lots of XDP codes since both
> > > mergeable and small buffer use page frag during refill now.
> > > 
> > >                         Before   | After
> > > XDP_DROP(xdp1) 64B  :  11.1Mpps | 14.4Mpps
> > > 
> > > Tested with xdp1/xdp2/xdp_ip_tx_tunnel and netperf.
> > > 
> > > Signed-off-by: Jason Wang<jasowang@...hat.com>
> > Thanks!
> > I had a similar patch for mergeable too, though it's trickier there
> > as host has a lot of flexibility in sizing buffers.
> > Looks like a good intermediate step to me.
> 
> Yes, I think it's more tricky for the case of mergeable buffer:
> 
> 1) we need reserve NET_SKB_PAD + NET_IP_ALIGN for each buffer, this will
> break rx frag coalescing
> 2) need tailroom for skb_shinfo, so it won't work for all size of packet
> 
> Thanks

Have you seen my prototype? It works with qemu in practice,
just needs to cover a bunch of corner cases.


> > 
> > 
> > Acked-by: Michael S. Tsirkin<mst@...hat.com>
> >