Re: [PATCH net-next v2] vhost/net: Defer TX queue re-enable until after sendmsg

[Paolo Abeni <pabeni@redhat.com>]

On 4/20/25 3:05 AM, Jon Kohler wrote:
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index b9b9e9d40951..9b04025eea66 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -769,13 +769,17 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
>  			break;
>  		/* Nothing new?  Wait for eventfd to tell us they refilled. */
>  		if (head == vq->num) {
> +			/* If interrupted while doing busy polling, requeue
> +			 * the handler to be fair handle_rx as well as other
> +			 * tasks waiting on cpu
> +			 */
>  			if (unlikely(busyloop_intr)) {
>  				vhost_poll_queue(&vq->poll);
> -			} else if (unlikely(vhost_enable_notify(&net->dev,
> -								vq))) {
> -				vhost_disable_notify(&net->dev, vq);
> -				continue;
>  			}
> +			/* Kicks are disabled at this point, break loop and
> +			 * process any remaining batched packets. Queue will
> +			 * be re-enabled afterwards.
> +			 */
>  			break;
>  		}

It's not clear to me why the zerocopy path does not need a similar change.

> @@ -825,7 +829,14 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
>  		++nvq->done_idx;
>  	} while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));
>  
> +	/* Kicks are still disabled, dispatch any remaining batched msgs. */
>  	vhost_tx_batch(net, nvq, sock, &msg);
> +
> +	/* All of our work has been completed; however, before leaving the
> +	 * TX handler, do one last check for work, and requeue handler if
> +	 * necessary. If there is no work, queue will be reenabled.
> +	 */
> +	vhost_net_busy_poll_try_queue(net, vq);

This will call vhost_poll_queue() regardless of the 'busyloop_intr' flag
value, while AFAICS prior to this patch vhost_poll_queue() is only
performed with busyloop_intr == true. Why don't we need to take care of
such flag here?

@Michael: I assume you prefer that this patch will go through the
net-next tree, right?

Thanks,

Paolo