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Message-ID: <20130310165030.GA13687@redhat.com>
Date: Sun, 10 Mar 2013 18:50:30 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost_net: remove tx polling state
On Thu, Mar 07, 2013 at 12:31:56PM +0800, Jason Wang wrote:
> After commit 2b8b328b61c799957a456a5a8dab8cc7dea68575 (vhost_net: handle polling
> errors when setting backend), we in fact track the polling state through
> poll->wqh, so there's no need to duplicate the work with an extra
> vhost_net_polling_state. So this patch removes this and make the code simpler.
>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
I'd prefer a more radical approach, since I think it can be even
simpler: tap and macvtap backends both only send events when tx queue
overruns which should almost never happen.
So let's just start polling when VQ is enabled
drop all poll_start/stop calls on data path.
The optimization was written for packet socket backend but I know of no
one caring about performance of that one that much.
Needs a bit of perf testing to make sure I didn't miss anything though
but it's not 3.9 material anyway so there's no rush.
> ---
> drivers/vhost/net.c | 60 ++++++++----------------------------------------
> drivers/vhost/vhost.c | 3 ++
> 2 files changed, 13 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 959b1cd..d1a03dd 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -64,20 +64,10 @@ enum {
> VHOST_NET_VQ_MAX = 2,
> };
>
> -enum vhost_net_poll_state {
> - VHOST_NET_POLL_DISABLED = 0,
> - VHOST_NET_POLL_STARTED = 1,
> - VHOST_NET_POLL_STOPPED = 2,
> -};
> -
> struct vhost_net {
> struct vhost_dev dev;
> struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX];
> struct vhost_poll poll[VHOST_NET_VQ_MAX];
> - /* Tells us whether we are polling a socket for TX.
> - * We only do this when socket buffer fills up.
> - * Protected by tx vq lock. */
> - enum vhost_net_poll_state tx_poll_state;
> /* Number of TX recently submitted.
> * Protected by tx vq lock. */
> unsigned tx_packets;
> @@ -155,28 +145,6 @@ static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
> }
> }
>
> -/* Caller must have TX VQ lock */
> -static void tx_poll_stop(struct vhost_net *net)
> -{
> - if (likely(net->tx_poll_state != VHOST_NET_POLL_STARTED))
> - return;
> - vhost_poll_stop(net->poll + VHOST_NET_VQ_TX);
> - net->tx_poll_state = VHOST_NET_POLL_STOPPED;
> -}
> -
> -/* Caller must have TX VQ lock */
> -static int tx_poll_start(struct vhost_net *net, struct socket *sock)
> -{
> - int ret;
> -
> - if (unlikely(net->tx_poll_state != VHOST_NET_POLL_STOPPED))
> - return 0;
> - ret = vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file);
> - if (!ret)
> - net->tx_poll_state = VHOST_NET_POLL_STARTED;
> - return ret;
> -}
> -
> /* In case of DMA done not in order in lower device driver for some reason.
> * upend_idx is used to track end of used idx, done_idx is used to track head
> * of used idx. Once lower device DMA done contiguously, we will signal KVM
> @@ -231,6 +199,7 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
> static void handle_tx(struct vhost_net *net)
> {
> struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
> + struct vhost_poll *poll = net->poll + VHOST_NET_VQ_TX;
> unsigned out, in, s;
> int head;
> struct msghdr msg = {
> @@ -256,7 +225,7 @@ static void handle_tx(struct vhost_net *net)
> wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> if (wmem >= sock->sk->sk_sndbuf) {
> mutex_lock(&vq->mutex);
> - tx_poll_start(net, sock);
> + vhost_poll_start(poll, sock->file);
> mutex_unlock(&vq->mutex);
> return;
> }
> @@ -265,7 +234,7 @@ static void handle_tx(struct vhost_net *net)
> vhost_disable_notify(&net->dev, vq);
>
> if (wmem < sock->sk->sk_sndbuf / 2)
> - tx_poll_stop(net);
> + vhost_poll_stop(poll);
> hdr_size = vq->vhost_hlen;
> zcopy = vq->ubufs;
>
> @@ -287,7 +256,7 @@ static void handle_tx(struct vhost_net *net)
>
> wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> if (wmem >= sock->sk->sk_sndbuf * 3 / 4) {
> - tx_poll_start(net, sock);
> + vhost_poll_start(poll, sock->file);
> set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
> break;
> }
> @@ -298,7 +267,7 @@ static void handle_tx(struct vhost_net *net)
> (vq->upend_idx - vq->done_idx) :
> (vq->upend_idx + UIO_MAXIOV - vq->done_idx);
> if (unlikely(num_pends > VHOST_MAX_PEND)) {
> - tx_poll_start(net, sock);
> + vhost_poll_start(poll, sock->file);
> set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
> break;
> }
> @@ -364,7 +333,7 @@ static void handle_tx(struct vhost_net *net)
> }
> vhost_discard_vq_desc(vq, 1);
> if (err == -EAGAIN || err == -ENOBUFS)
> - tx_poll_start(net, sock);
> + vhost_poll_start(poll, sock->file);
> break;
> }
> if (err != len)
> @@ -627,7 +596,6 @@ static int vhost_net_open(struct inode *inode, struct file *f)
>
> vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev);
> vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev);
> - n->tx_poll_state = VHOST_NET_POLL_DISABLED;
>
> f->private_data = n;
>
> @@ -637,32 +605,24 @@ static int vhost_net_open(struct inode *inode, struct file *f)
> static void vhost_net_disable_vq(struct vhost_net *n,
> struct vhost_virtqueue *vq)
> {
> + struct vhost_poll *poll = n->poll + (vq - n->vqs);
> if (!vq->private_data)
> return;
> - if (vq == n->vqs + VHOST_NET_VQ_TX) {
> - tx_poll_stop(n);
> - n->tx_poll_state = VHOST_NET_POLL_DISABLED;
> - } else
> - vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
> + vhost_poll_stop(poll);
> }
>
> static int vhost_net_enable_vq(struct vhost_net *n,
> struct vhost_virtqueue *vq)
> {
> + struct vhost_poll *poll = n->poll + (vq - n->vqs);
> struct socket *sock;
> - int ret;
>
> sock = rcu_dereference_protected(vq->private_data,
> lockdep_is_held(&vq->mutex));
> if (!sock)
> return 0;
> - if (vq == n->vqs + VHOST_NET_VQ_TX) {
> - n->tx_poll_state = VHOST_NET_POLL_STOPPED;
> - ret = tx_poll_start(n, sock);
> - } else
> - ret = vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
>
> - return ret;
> + return vhost_poll_start(poll, sock->file);
> }
>
> static struct socket *vhost_net_stop_vq(struct vhost_net *n,
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 9759249..4eecdb8 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -89,6 +89,9 @@ int vhost_poll_start(struct vhost_poll *poll, struct file *file)
> unsigned long mask;
> int ret = 0;
>
> + if (poll->wqh)
> + return 0;
> +
> mask = file->f_op->poll(file, &poll->table);
> if (mask)
> vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
> --
> 1.7.1
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