netdev - Re: [PATCH net-next] tuntap: XDP

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Date:   Thu, 15 Mar 2018 15:32:06 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] tuntap: XDP_TX can use native XDP

On Thu, Mar 15, 2018 at 04:39:25PM +0800, Jason Wang wrote:
> 
> 
> On 2018年03月14日 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?