On Wed, Sep 17, 2025 at 8:31 AM Jason Wang <jasow...@redhat.com> wrote:
>
> Commit 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after
> sendmsg") tries to defer the notification enabling by moving the logic
> out of the loop after the vhost_tx_batch() when nothing new is spotted.
> This caused unexpected side effects as the new logic is reused for
> several other error conditions.
>
> A previous patch reverted 8c2e6b26ffe2. Now, bring the performance
> back up by flushing batched buffers before enabling notifications.
>
Acked-by: Eugenio Pérez <epere...@redhat.com>
> Reported-by: Jon Kohler <j...@nutanix.com>
> Cc: sta...@vger.kernel.org
> Fixes: 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after
> sendmsg")
> Signed-off-by: Jason Wang <jasow...@redhat.com>
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> ---
> drivers/vhost/net.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 57efd5c55f89..35ded4330431 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -780,6 +780,11 @@ static void handle_tx_copy(struct vhost_net *net, struct
> socket *sock)
The same optimization can be done in handle_tx_zerocopy, should it be
marked as TODO?
I guess a lot of logic could be reused from one function to the other
or, ideally, merging both handle_tx_zerocopy and handle_tx_copy.
But it is better to do it on top.
> break;
> /* Nothing new? Wait for eventfd to tell us they refilled. */
> if (head == vq->num) {
> + /* Flush batched packets to handle pending RX
> + * work (if busyloop_intr is set) and to avoid
> + * unnecessary virtqueue kicks.
> + */
> + vhost_tx_batch(net, nvq, sock, &msg);
> if (unlikely(busyloop_intr)) {
> vhost_poll_queue(&vq->poll);
> } else if (unlikely(vhost_enable_notify(&net->dev,
> --
> 2.34.1
>
