On Tue, Oct 31, 2017 at 06:27:20PM +0800, Jason Wang wrote:
> We always poll tx for socket, this is sub optimal since:
>
> - we only want to be notified when sndbuf is available
> - this will slightly increase the waitqueue traversing time and more
> important, vhost could not benefit from commit
> commit 9e641bdcfa4e
> ("net-tun: restructure tun_do_read for better sleep/wakeup efficiency")
> even if we've stopped rx polling during handle_rx() since tx poll
> were still left in the waitqueue.
>
> Pktgen from a remote host to VM over mlx4 shows 5.5% improvements on
> rx PPS. (from 1.27Mpps to 1.34Mpps)
>
> Cc: Wei Xu <wexu@xxxxxxxxxx>
> Cc: Matthew Rosato <mjrosato@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
Now that vhost_poll_stop happens on data path
a lot, I'd say
if (poll->wqh)
there should be unlikely().
> drivers/vhost/net.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 68677d9..286c3e4 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -471,6 +471,7 @@ static void handle_tx(struct vhost_net *net)
> goto out;
>
> vhost_disable_notify(&net->dev, vq);
> + vhost_net_disable_vq(net, vq);
>
> hdr_size = nvq->vhost_hlen;
> zcopy = nvq->ubufs;
> @@ -556,6 +557,8 @@ static void handle_tx(struct vhost_net *net)
> % UIO_MAXIOV;
> }
> vhost_discard_vq_desc(vq, 1);
> + if (err == -EAGAIN)
> + vhost_net_enable_vq(net, vq);
> break;
> }
> if (err != len)
I would probably just enable it unconditionally here. Why not?
> @@ -1145,9 +1148,11 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
> r = vhost_vq_init_access(vq);
> if (r)
> goto err_used;
> - r = vhost_net_enable_vq(n, vq);
> - if (r)
> - goto err_used;
> + if (index == VHOST_NET_VQ_RX) {
> + r = vhost_net_enable_vq(n, vq);
> + if (r)
> + goto err_used;
> + }
>
> oldubufs = nvq->ubufs;
> nvq->ubufs = ubufs;
This last chunk seems questionable. If queue has stuff in it
when we connect the backend, we'll miss a wakeup.
I suspect this can happen during migration.
> --
> 2.7.4
