From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH net-next] tuntap: XDP_TX can use native XDP
Date: Thu, 15 Mar 2018 15:32:06 +0200
Message-ID: <20180315153150-mutt-send-email-mst@kernel.org>
References: <1520997820-8289-1-git-send-email-jasowang@redhat.com>
 <20180314053424-mutt-send-email-mst@kernel.org>
 <21e53c2b-6677-fc9a-0771-e895da1c257f@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org
To: Jason Wang <jasowang@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <21e53c2b-6677-fc9a-0771-e895da1c257f@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

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?