Re: [PATCH net-next] tuntap: XDP_TX can use native XDP

[Jason Wang]

On 2018å03æ15æ 21:32, Michael S. Tsirkin wrote:
> On Thu, Mar 15, 2018 at 04:39:25PM +0800, Jason Wang wrote:
> > On 2018å03æ14æ 11:37, Michael S. Tsirkin wrote:
> > > >    			return NULL;
> > > >    		case XDP_TX:
> > > > -			xdp_xmit = true;
> > > > -			/* fall through */
> > > > +			get_page(alloc_frag->page);
> > > > +			alloc_frag->offset += buflen;
> > > > +			if (tun_xdp_xmit(tun->dev, &xdp))
> > > > +				goto err_redirect;
> > > > +			tun_xdp_flush(tun->dev);
> > > Why do we have to flush here though?
> > > It might be a good idea to document the reason in a code comment.
> > ndo_xdp_xmit() does not touch doorbell, so we need a ndo_xdp_flush() here.
> > It's the assumption of XDP API I think, so not sure it's worth to mention it
> > here.
> >
> > Thanks
> Can't one flush we called after multiple xmit calls?

We can and could be another patch on top. But I want to unify it with 
the batching of XDP_REDIRECT by e.g let vhost submit more than one 
packets through msg.control in sendmsg().

Thanks