Subject: Re: [PATCH v1 2/3] Provides multiple submits and asynchronous notifications.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 16 Mar 2010 13:33:16 +0200

On Tue, Mar 16, 2010 at 05:32:17PM +0800, Xin Xiaohui wrote:
> The vhost-net backend now only supports synchronous send/recv
> operations. The patch provides multiple submits and asynchronous
> notifications. This is needed for zero-copy case.
> 
> Signed-off-by: Xin Xiaohui <[email-masked]>
> ---
> 
> Michael,
> I don't use the kiocb comes from the sendmsg/recvmsg,
> since I have embeded the kiocb in page_info structure,
> and allocate it when page_info allocated.

So what I suggested was that vhost allocates and tracks the iocbs, and
passes them to your device with sendmsg/ recvmsg calls. This way your
device won't need to share structures and locking strategy with vhost:
you get an iocb, handle it, invoke a callback to notify vhost about
completion.

This also gets rid of the 'receiver' callback.

> Please have a review and thanks for the instruction
> for replying email which helps me a lot.
> 
> Thanks,
> Xiaohui
> 
>  drivers/vhost/net.c   |  159 +++++++++++++++++++++++++++++++++++++++++++++++--
>  drivers/vhost/vhost.h |   12 ++++
>  2 files changed, 166 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 22d5fef..5483848 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -17,11 +17,13 @@
>  #include <linux/workqueue.h>
>  #include <linux/rcupdate.h>
>  #include <linux/file.h>
> +#include <linux/aio.h>
>  
>  #include <linux/net.h>
>  #include <linux/if_packet.h>
>  #include <linux/if_arp.h>
>  #include <linux/if_tun.h>
> +#include <linux/mpassthru.h>
>  
>  #include <net/sock.h>
>  
> @@ -91,6 +93,12 @@ static void tx_poll_start(struct vhost_net *net, struct socket *sock)
>  	net->tx_poll_state = VHOST_NET_POLL_STARTED;
>  }
>  
> +static void handle_async_rx_events_notify(struct vhost_net *net,
> +					struct vhost_virtqueue *vq);
> +
> +static void handle_async_tx_events_notify(struct vhost_net *net,
> +					struct vhost_virtqueue *vq);
> +

A couple of style comments:

- It's better to arrange functions in such order that forward declarations
aren't necessary.  Since we don't have recursion, this should always be
possible.

- continuation lines should be idented at least at the position of '('
on the previous line.

>  /* Expects to be always run from workqueue - which acts as
>   * read-size critical section for our kind of RCU. */
>  static void handle_tx(struct vhost_net *net)
> @@ -124,6 +132,8 @@ static void handle_tx(struct vhost_net *net)
>  		tx_poll_stop(net);
>  	hdr_size = vq->hdr_size;
>  
> +	handle_async_tx_events_notify(net, vq);
> +
>  	for (;;) {
>  		head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
>  					 ARRAY_SIZE(vq->iov),
> @@ -151,6 +161,12 @@ static void handle_tx(struct vhost_net *net)
>  		/* Skip header. TODO: support TSO. */
>  		s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, out);
>  		msg.msg_iovlen = out;
> +
> +		if (vq->link_state == VHOST_VQ_LINK_ASYNC) {
> +			vq->head = head;
> +			msg.msg_control = (void *)vq;

So here a device gets a pointer to vhost_virtqueue structure. If it gets
an iocb and invokes a callback, it would not care about vhost internals.

> +		}
> +
>  		len = iov_length(vq->iov, out);
>  		/* Sanity check */
>  		if (!len) {
> @@ -166,6 +182,10 @@ static void handle_tx(struct vhost_net *net)
>  			tx_poll_start(net, sock);
>  			break;
>  		}
> +
> +		if (vq->link_state == VHOST_VQ_LINK_ASYNC)
> +			continue;
> +
>  		if (err != len)
>  			pr_err("Truncated TX packet: "
>  			       " len %d != %zd\n", err, len);
> @@ -177,6 +197,8 @@ static void handle_tx(struct vhost_net *net)
>  		}
>  	}
>  
> +	handle_async_tx_events_notify(net, vq);
> +
>  	mutex_unlock(&vq->mutex);
>  	unuse_mm(net->dev.mm);
>  }
> @@ -206,7 +228,8 @@ static void handle_rx(struct vhost_net *net)
>  	int err;
>  	size_t hdr_size;
>  	struct socket *sock = rcu_dereference(vq->private_data);
> -	if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
> +	if (!sock || (skb_queue_empty(&sock->sk->sk_receive_queue) &&
> +			vq->link_state == VHOST_VQ_LINK_SYNC))
>  		return;
>  
>  	use_mm(net->dev.mm);
> @@ -214,9 +237,18 @@ static void handle_rx(struct vhost_net *net)
>  	vhost_disable_notify(vq);
>  	hdr_size = vq->hdr_size;
>  
> -	vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
> +	/* In async cases, for write logging, the simple way is to get
> +	 * the log info always, and really logging is decided later.
> +	 * Thus, when logging enabled, we can get log, and when logging
> +	 * disabled, we can get log disabled accordingly.
> +	 */
> +

This adds overhead and might be one of the reasons
your patch does not perform that well. A better way
would be to flush outstanding requests or reread the vq
when logging is enabled.

> +	vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) |
> +		(vq->link_state == VHOST_VQ_LINK_ASYNC) ?
>  		vq->log : NULL;
>  
> +	handle_async_rx_events_notify(net, vq);
> +
>  	for (;;) {
>  		head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
>  					 ARRAY_SIZE(vq->iov),
> @@ -245,6 +277,11 @@ static void handle_rx(struct vhost_net *net)
>  		s = move_iovec_hdr(vq->iov, vq->hdr, hdr_size, in);
>  		msg.msg_iovlen = in;
>  		len = iov_length(vq->iov, in);
> +		if (vq->link_state == VHOST_VQ_LINK_ASYNC) {
> +			vq->head = head;
> +			vq->_log = log;
> +			msg.msg_control = (void *)vq;
> +		}
>  		/* Sanity check */
>  		if (!len) {
>  			vq_err(vq, "Unexpected header len for RX: "
> @@ -259,6 +296,10 @@ static void handle_rx(struct vhost_net *net)
>  			vhost_discard_vq_desc(vq);
>  			break;
>  		}
> +
> +		if (vq->link_state == VHOST_VQ_LINK_ASYNC)
> +			continue;
> +
>  		/* TODO: Should check and handle checksum. */
>  		if (err > len) {
>  			pr_err("Discarded truncated rx packet: "
> @@ -284,10 +325,85 @@ static void handle_rx(struct vhost_net *net)
>  		}
>  	}
>  
> +	handle_async_rx_events_notify(net, vq);
> +
>  	mutex_unlock(&vq->mutex);
>  	unuse_mm(net->dev.mm);
>  }
>  
> +struct kiocb *notify_dequeue(struct vhost_virtqueue *vq)
> +{
> +	struct kiocb *iocb = NULL;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&vq->notify_lock, flags);
> +	if (!list_empty(&vq->notifier)) {
> +		iocb = list_first_entry(&vq->notifier,
> +				struct kiocb, ki_list);
> +		list_del(&iocb->ki_list);
> +	}
> +	spin_unlock_irqrestore(&vq->notify_lock, flags);
> +	return iocb;
> +}
> +
> +static void handle_async_rx_events_notify(struct vhost_net *net,
> +				struct vhost_virtqueue *vq)
> +{
> +	struct kiocb *iocb = NULL;
> +	struct vhost_log *vq_log = NULL;
> +	int rx_total_len = 0;
> +	int log, size;
> +
> +	if (vq->link_state != VHOST_VQ_LINK_ASYNC)
> +		return;
> +	if (vq != &net->dev.vqs[VHOST_NET_VQ_RX])
> +		return;
> +
> +	if (vq->receiver)
> +		vq->receiver(vq);
> +	vq_log = unlikely(vhost_has_feature(
> +				&net->dev, VHOST_F_LOG_ALL)) ? vq->log : NULL;
> +	while ((iocb = notify_dequeue(vq)) != NULL) {
> +		vhost_add_used_and_signal(&net->dev, vq,
> +				iocb->ki_pos, iocb->ki_nbytes);
> +		log = (int)iocb->ki_user_data;
> +		size = iocb->ki_nbytes;
> +		rx_total_len += iocb->ki_nbytes;
> +		if (iocb->ki_dtor)
> +			iocb->ki_dtor(iocb);
> +		if (unlikely(vq_log))
> +			vhost_log_write(vq, vq_log, log, size);
> +		if (unlikely(rx_total_len >= VHOST_NET_WEIGHT)) {
> +			vhost_poll_queue(&vq->poll);
> +			break;
> +		}
> +	}
> +}
> +
> +static void handle_async_tx_events_notify(struct vhost_net *net,
> +		struct vhost_virtqueue *vq)
> +{
> +	struct kiocb *iocb = NULL;
> +	int tx_total_len = 0;
> +
> +	if (vq->link_state != VHOST_VQ_LINK_ASYNC)
> +		return;
> +	if (vq != &net->dev.vqs[VHOST_NET_VQ_TX])
> +		return;
> +

Hard to see why the second check would be necessary

> +	while ((iocb = notify_dequeue(vq)) != NULL) {
> +		vhost_add_used_and_signal(&net->dev, vq,
> +				iocb->ki_pos, 0);
> +		tx_total_len += iocb->ki_nbytes;
> +		if (iocb->ki_dtor)
> +			iocb->ki_dtor(iocb);
> +		if (unlikely(tx_total_len >= VHOST_NET_WEIGHT)) {
> +			vhost_poll_queue(&vq->poll);
> +			break;
> +		}
> +	}
> +}
> +
>  static void handle_tx_kick(struct work_struct *work)
>  {
>  	struct vhost_virtqueue *vq;
> @@ -462,7 +578,19 @@ static struct socket *get_tun_socket(int fd)
>  	return sock;
>  }
>  
> -static struct socket *get_socket(int fd)
> +static struct socket *get_mp_socket(int fd)
> +{
> +	struct file *file = fget(fd);
> +	struct socket *sock;
> +	if (!file)
> +		return ERR_PTR(-EBADF);
> +	sock = mp_get_socket(file);
> +	if (IS_ERR(sock))
> +		fput(file);
> +	return sock;
> +}
> +
> +static struct socket *get_socket(struct vhost_virtqueue *vq, int fd)
>  {
>  	struct socket *sock;
>  	if (fd == -1)
> @@ -473,9 +601,26 @@ static struct socket *get_socket(int fd)
>  	sock = get_tun_socket(fd);
>  	if (!IS_ERR(sock))
>  		return sock;
> +	sock = get_mp_socket(fd);
> +	if (!IS_ERR(sock)) {
> +		vq->link_state = VHOST_VQ_LINK_ASYNC;
> +		return sock;
> +	}
>  	return ERR_PTR(-ENOTSOCK);
>  }
>  
> +static void vhost_init_link_state(struct vhost_net *n, int index)
> +{
> +	struct vhost_virtqueue *vq = n->vqs + index;
> +
> +	WARN_ON(!mutex_is_locked(&vq->mutex));
> +	if (vq->link_state == VHOST_VQ_LINK_ASYNC) {
> +		vq->receiver = NULL;
> +		INIT_LIST_HEAD(&vq->notifier);
> +		spin_lock_init(&vq->notify_lock);
> +	}
> +}
> +
>  static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
>  {
>  	struct socket *sock, *oldsock;
> @@ -493,12 +638,15 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
>  	}
>  	vq = n->vqs + index;
>  	mutex_lock(&vq->mutex);
> -	sock = get_socket(fd);
> +	vq->link_state = VHOST_VQ_LINK_SYNC;
> +	sock = get_socket(vq, fd);
>  	if (IS_ERR(sock)) {
>  		r = PTR_ERR(sock);
>  		goto err;
>  	}
>  
> +	vhost_init_link_state(n, index);
> +
>  	/* start polling new socket */
>  	oldsock = vq->private_data;
>  	if (sock == oldsock)
> @@ -507,8 +655,8 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
>  	vhost_net_disable_vq(n, vq);
>  	rcu_assign_pointer(vq->private_data, sock);
>  	vhost_net_enable_vq(n, vq);
> -	mutex_unlock(&vq->mutex);
>  done:
> +	mutex_unlock(&vq->mutex);
>  	mutex_unlock(&n->dev.mutex);
>  	if (oldsock) {
>  		vhost_net_flush_vq(n, index);
> @@ -516,6 +664,7 @@ done:
>  	}
>  	return r;
>  err:
> +	mutex_unlock(&vq->mutex);
>  	mutex_unlock(&n->dev.mutex);
>  	return r;
>  }
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index d1f0453..297af1c 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -43,6 +43,11 @@ struct vhost_log {
>  	u64 len;
>  };
>  
> +enum vhost_vq_link_state {
> +	VHOST_VQ_LINK_SYNC = 	0,
> +	VHOST_VQ_LINK_ASYNC = 	1,
> +};
> +
>  /* The virtqueue structure describes a queue attached to a device. */
>  struct vhost_virtqueue {
>  	struct vhost_dev *dev;
> @@ -96,6 +101,13 @@ struct vhost_virtqueue {
>  	/* Log write descriptors */
>  	void __user *log_base;
>  	struct vhost_log log[VHOST_NET_MAX_SG];
> +	/*Differiate async socket for 0-copy from normal*/
> +	enum vhost_vq_link_state link_state;
> +	int head;
> +	int _log;
> +	struct list_head notifier;
> +	spinlock_t notify_lock;
> +	void (*receiver)(struct vhost_virtqueue *);
>  };
>  
>  struct vhost_dev {
> -- 
> 1.5.4.4