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Message-ID: <30e62749-3cbd-ae88-6582-c20087884b20@redhat.com>
Date: Wed, 1 Aug 2018 14:01:23 +0800
From: Jason Wang <jasowang@...hat.com>
To: xiangxia.m.yue@...il.com
Cc: mst@...hat.com, makita.toshiaki@....ntt.co.jp,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v7 3/4] net: vhost: factor out busy polling logic
to vhost_net_busy_poll()
On 2018年08月01日 11:00, 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.
>
> In the handle_tx, the busypoll will vhost_net_disable/enable_vq
> because we have poll the sock. This can improve performance.
> [This is suggested by Toshiaki Makita <makita.toshiaki@....ntt.co.jp>]
>
> And when the sock receive skb, we should queue the poll if necessary.
>
> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> ---
> drivers/vhost/net.c | 131 ++++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 91 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 32c1b52..5b45463 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -440,6 +440,95 @@ static void vhost_net_signal_used(struct vhost_net_virtqueue *nvq)
> nvq->done_idx = 0;
> }
>
> +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_try_queue(struct vhost_net *net,
> + struct vhost_virtqueue *vq)
> +{
> + 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);
> + }
> +}
> +
> +static void vhost_net_busy_poll_check(struct vhost_net *net,
> + struct vhost_virtqueue *rvq,
> + struct vhost_virtqueue *tvq,
> + bool rx)
> +{
> + struct socket *sock = rvq->private_data;
> +
> + if (rx)
> + vhost_net_busy_poll_try_queue(net, tvq);
> + else if (sock && sk_has_rx_data(sock->sk))
> + vhost_net_busy_poll_try_queue(net, rvq);
> + else {
> + /* On tx here, sock has no rx data, so we
> + * will wait for sock wakeup for rx, and
> + * vhost_enable_notify() is not needed. */
A possible case is we do have rx data but guest does not refill the rx
queue. In this case we may lose notifications from guest.
> + }
> +}
> +
> +static void vhost_net_busy_poll(struct vhost_net *net,
> + struct vhost_virtqueue *rvq,
> + struct vhost_virtqueue *tvq,
> + bool *busyloop_intr,
> + bool rx)
> +{
> + unsigned long busyloop_timeout;
> + unsigned long endtime;
> + 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;
> +
> +
> + /* Busypoll the sock, so don't need rx wakeups during it. */
> + if (!rx)
> + vhost_net_disable_vq(net, vq);
Actually this piece of code is not a factoring out. I would suggest to
add this in another patch, or on top of this series.
> +
> + preempt_disable();
> + endtime = busy_clock() + busyloop_timeout;
> +
> + while (vhost_can_busy_poll(endtime)) {
> + if (vhost_has_work(&net->dev)) {
> + *busyloop_intr = true;
> + break;
> + }
> +
> + if ((sock && sk_has_rx_data(sock->sk) &&
> + !vhost_vq_avail_empty(&net->dev, rvq)) ||
> + !vhost_vq_avail_empty(&net->dev, tvq))
> + break;
Some checks were duplicated in vhost_net_busy_poll_check(). Need
consider to unify them.
> +
> + cpu_relax();
> + }
> +
> + preempt_enable();
> +
> + if (!rx)
> + vhost_net_enable_vq(net, vq);
No need to enable rx virtqueue, if we are sure handle_rx() will be
called soon.
> +
> + vhost_net_busy_poll_check(net, rvq, tvq, rx);
It looks to me just open code all check here is better and easier to be
reviewed.
Thanks
> +
> + mutex_unlock(&vq->mutex);
> +}
> +
> static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
> struct vhost_net_virtqueue *nvq,
> unsigned int *out_num, unsigned int *in_num,
> @@ -753,16 +842,6 @@ 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 int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> bool *busyloop_intr)
> {
> @@ -770,41 +849,13 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
> struct vhost_virtqueue *rvq = &rnvq->vq;
> struct vhost_virtqueue *tvq = &tnvq->vq;
> - unsigned long uninitialized_var(endtime);
> int len = peek_head_len(rnvq, sk);
>
> - if (!len && tvq->busyloop_timeout) {
> + if (!len && rvq->busyloop_timeout) {
> /* Flush batched heads first */
> vhost_net_signal_used(rnvq);
> /* Both tx vq and rx socket were polled here */
> - mutex_lock_nested(&tvq->mutex, VHOST_NET_VQ_TX);
> - vhost_disable_notify(&net->dev, tvq);
> -
> - preempt_disable();
> - endtime = busy_clock() + tvq->busyloop_timeout;
> -
> - while (vhost_can_busy_poll(endtime)) {
> - if (vhost_has_work(&net->dev)) {
> - *busyloop_intr = true;
> - break;
> - }
> - if ((sk_has_rx_data(sk) &&
> - !vhost_vq_avail_empty(&net->dev, rvq)) ||
> - !vhost_vq_avail_empty(&net->dev, tvq))
> - break;
> - cpu_relax();
> - }
> -
> - preempt_enable();
> -
> - if (!vhost_vq_avail_empty(&net->dev, tvq)) {
> - vhost_poll_queue(&tvq->poll);
> - } else if (unlikely(vhost_enable_notify(&net->dev, tvq))) {
> - vhost_disable_notify(&net->dev, tvq);
> - vhost_poll_queue(&tvq->poll);
> - }
> -
> - mutex_unlock(&tvq->mutex);
> + vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, true);
>
> len = peek_head_len(rnvq, sk);
> }
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