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

On 2018年03月15日 21:32, Michael S. Tsirkin wrote:

On Thu, Mar 15, 2018 at 04:39:25PM +0800, Jason Wang wrote:

quoted

On 2018年03月14日 11:37, Michael S. Tsirkin wrote:

quoted

quoted

   			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