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Date: Wed, 4 Jul 2018 09:40:31 +0800
From: Tonghao Zhang <xiangxia.m.yue@...il.com>
To: jasowang@...hat.com
Cc: mst@...hat.com, makita.toshiaki@....ntt.co.jp,
virtualization@...ts.linux-foundation.org,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
Tonghao Zhang <zhangtonghao@...ichuxing.com>
Subject: Re: [PATCH net-next v4 3/4] net: vhost: factor out busy polling logic
to vhost_net_busy_poll()
On Tue, Jul 3, 2018 at 1:55 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
>
> On 2018年07月03日 13:48, Tonghao Zhang wrote:
> > On Tue, Jul 3, 2018 at 10:12 AM Jason Wang <jasowang@...hat.com> wrote:
> >>
> >>
> >> On 2018年07月02日 20:57, xiangxia.m.yue@...il.com wrote:
> >>> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> >>>
> >>> Factor out generic busy polling logic and will be
> >>> used for in tx path in the next patch. And with the patch,
> >>> qemu can set differently the busyloop_timeout for rx queue.
> >>>
> >>> Signed-off-by: Tonghao Zhang <zhangtonghao@...ichuxing.com>
> >>> ---
> >>> drivers/vhost/net.c | 94 +++++++++++++++++++++++++++++++----------------------
> >>> 1 file changed, 55 insertions(+), 39 deletions(-)
> >>>
> >>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> >>> index 62bb8e8..2790959 100644
> >>> --- a/drivers/vhost/net.c
> >>> +++ b/drivers/vhost/net.c
> >>> @@ -429,6 +429,52 @@ static int vhost_net_enable_vq(struct vhost_net *n,
> >>> return vhost_poll_start(poll, sock->file);
> >>> }
> >>>
> >>> +static int sk_has_rx_data(struct sock *sk)
> >>> +{
> >>> + struct socket *sock = sk->sk_socket;
> >>> +
> >>> + if (sock->ops->peek_len)
> >>> + return sock->ops->peek_len(sock);
> >>> +
> >>> + return skb_queue_empty(&sk->sk_receive_queue);
> >>> +}
> >>> +
> >>> +static void vhost_net_busy_poll(struct vhost_net *net,
> >>> + struct vhost_virtqueue *rvq,
> >>> + struct vhost_virtqueue *tvq,
> >>> + bool rx)
> >>> +{
> >>> + unsigned long uninitialized_var(endtime);
> >>> + unsigned long busyloop_timeout;
> >>> + struct socket *sock;
> >>> + struct vhost_virtqueue *vq = rx ? tvq : rvq;
> >>> +
> >>> + mutex_lock_nested(&vq->mutex, rx ? VHOST_NET_VQ_TX: VHOST_NET_VQ_RX);
> >>> +
> >>> + vhost_disable_notify(&net->dev, vq);
> >>> + sock = rvq->private_data;
> >>> + busyloop_timeout = rx ? rvq->busyloop_timeout : tvq->busyloop_timeout;
> >>> +
> >>> + preempt_disable();
> >>> + endtime = busy_clock() + busyloop_timeout;
> >>> + while (vhost_can_busy_poll(tvq->dev, endtime) &&
> >>> + !(sock && sk_has_rx_data(sock->sk)) &&
> >>> + vhost_vq_avail_empty(tvq->dev, tvq))
> >>> + cpu_relax();
> >>> + preempt_enable();
> >>> +
> >>> + if ((rx && !vhost_vq_avail_empty(&net->dev, vq)) ||
> >>> + (!rx && (sock && sk_has_rx_data(sock->sk)))) {
> >>> + vhost_poll_queue(&vq->poll);
> >>> + } else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> >> One last question, do we need this for rx? This check will be always
> >> true under light or medium load.
> > will remove the 'unlikely'
>
> Not only the unlikely. We only want rx kick when packet is pending at
> socket but we're out of available buffers. This is not the case here
> (you have polled the vq above).
>
> So we probably want to do this only when rx == true.
got it. change it to:
+ } else if (vhost_enable_notify(&net->dev, vq) && rx) {
+ vhost_disable_notify(&net->dev, vq);
+ vhost_poll_queue(&vq->poll);
+ }
> Thanks
>
> >
> >> Thanks
> >>
> >>> + vhost_disable_notify(&net->dev, vq);
> >>> + vhost_poll_queue(&vq->poll);
> >>> + }
> >>> +
> >>> + mutex_unlock(&vq->mutex);
> >>> +}
> >>> +
> >>> +
> >>> static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
> >>> struct vhost_virtqueue *vq,
> >>> struct iovec iov[], unsigned int iov_size,
> >>> @@ -621,16 +667,6 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
> >>> return len;
> >>> }
> >>>
> >>> -static int sk_has_rx_data(struct sock *sk)
> >>> -{
> >>> - struct socket *sock = sk->sk_socket;
> >>> -
> >>> - if (sock->ops->peek_len)
> >>> - return sock->ops->peek_len(sock);
> >>> -
> >>> - return skb_queue_empty(&sk->sk_receive_queue);
> >>> -}
> >>> -
> >>> static void vhost_rx_signal_used(struct vhost_net_virtqueue *nvq)
> >>> {
> >>> struct vhost_virtqueue *vq = &nvq->vq;
> >>> @@ -645,39 +681,19 @@ static void vhost_rx_signal_used(struct vhost_net_virtqueue *nvq)
> >>>
> >>> static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
> >>> {
> >>> - struct vhost_net_virtqueue *rvq = &net->vqs[VHOST_NET_VQ_RX];
> >>> - struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
> >>> - struct vhost_virtqueue *vq = &nvq->vq;
> >>> - unsigned long uninitialized_var(endtime);
> >>> - int len = peek_head_len(rvq, sk);
> >>> + struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
> >>> + struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
> >>>
> >>> - if (!len && vq->busyloop_timeout) {
> >>> - /* Flush batched heads first */
> >>> - vhost_rx_signal_used(rvq);
> >>> - /* Both tx vq and rx socket were polled here */
> >>> - mutex_lock_nested(&vq->mutex, VHOST_NET_VQ_TX);
> >>> - vhost_disable_notify(&net->dev, vq);
> >>> + int len = peek_head_len(rnvq, sk);
> >>>
> >>> - preempt_disable();
> >>> - endtime = busy_clock() + vq->busyloop_timeout;
> >>> -
> >>> - while (vhost_can_busy_poll(&net->dev, endtime) &&
> >>> - !sk_has_rx_data(sk) &&
> >>> - vhost_vq_avail_empty(&net->dev, vq))
> >>> - cpu_relax();
> >>> -
> >>> - preempt_enable();
> >>> -
> >>> - if (!vhost_vq_avail_empty(&net->dev, vq))
> >>> - vhost_poll_queue(&vq->poll);
> >>> - else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> >>> - vhost_disable_notify(&net->dev, vq);
> >>> - vhost_poll_queue(&vq->poll);
> >>> - }
> >>> + if (!len && rnvq->vq.busyloop_timeout) {
> >>> + /* Flush batched heads first */
> >>> + vhost_rx_signal_used(rnvq);
> >>>
> >>> - mutex_unlock(&vq->mutex);
> >>> + /* Both tx vq and rx socket were polled here */
> >>> + vhost_net_busy_poll(net, &rnvq->vq, &tnvq->vq, true);
> >>>
> >>> - len = peek_head_len(rvq, sk);
> >>> + len = peek_head_len(rnvq, sk);
> >>> }
> >>>
> >>> return len;
>
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