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

[Jason Wang]

On 2017å02æ22æ 11:06, Michael S. Tsirkin wrote:
> On Wed, Feb 22, 2017 at 10:58:08AM +0800, Jason Wang wrote:
> > 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
> Have you seen my prototype?

Not yet, please give me a pointer.

>   It works with qemu in practice,
> just needs to cover a bunch of corner cases.

Sounds good, if you wish I can help to finalize it.

Thanks

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