Re: [PATCH net-next] virtio-net: switch to use build_skb() for small buffer

[Jason Wang]

On 2017å02æ21æ 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@xxxxxxxxxx>
> 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

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