Re: [PATCH v1 08/13] xen/pvcalls: implement sendmsg

[Stefano Stabellini]

On Mon, 24 Jul 2017, Juergen Gross wrote:
> On 22/07/17 02:11, Stefano Stabellini wrote:
> > Send data to an active socket by copying data to the "out" ring. Take
> > the active socket out_mutex so that only one function can access the
> > ring at any given time.
> > 
> > If not enough room is available on the ring, rather than returning
> > immediately or sleep-waiting, spin for up to 5000 cycles. This small
> > optimization turns out to improve performance significantly.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> > CC: boris.ostrovsky@xxxxxxxxxx
> > CC: jgross@xxxxxxxx
> > ---
> >  drivers/xen/pvcalls-front.c | 109 ++++++++++++++++++++++++++++++++++++++++++++
> >  drivers/xen/pvcalls-front.h |   3 ++
> >  2 files changed, 112 insertions(+)
> > 
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index f3a04a2..bf29f40 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -27,6 +27,7 @@
> >  #define PVCALLS_INVALID_ID (UINT_MAX)
> >  #define RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
> >  #define PVCALLS_NR_REQ_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)
> > +#define PVCALLS_FRON_MAX_SPIN 5000
> 
> Any reason not to name it PVCALLS_FRONT_MAX_SPIN? I first thought you
> meant FROM instead.

Clearly a typo :-)  I'll fix it.


> 
> >  
> >  struct pvcalls_bedata {
> >  	struct xen_pvcalls_front_ring ring;
> > @@ -77,6 +78,22 @@ struct sock_mapping {
> >  	};
> >  };
> >  
> > +static int pvcalls_front_write_todo(struct sock_mapping *map)
> > +{
> > +	struct pvcalls_data_intf *intf = map->active.ring;
> > +	RING_IDX cons, prod, size = XEN_FLEX_RING_SIZE(intf->ring_order);
> > +	int32_t error;
> > +
> > +	cons = intf->out_cons;
> > +	prod = intf->out_prod;
> > +	error = intf->out_error;
> > +	if (error == -ENOTCONN)
> > +		return 0;
> > +	if (error != 0)
> > +		return error;
> > +	return size - pvcalls_queued(prod, cons, size);
> > +}
> > +
> >  static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
> >  {
> >  	struct xenbus_device *dev = dev_id;
> > @@ -304,6 +321,98 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
> >  	return ret;
> >  }
> >  
> > +static int __write_ring(struct pvcalls_data_intf *intf,
> > +			struct pvcalls_data *data,
> > +			struct iov_iter *msg_iter,
> > +			size_t len)
> > +{
> > +	RING_IDX cons, prod, size, masked_prod, masked_cons;
> > +	RING_IDX array_size = XEN_FLEX_RING_SIZE(intf->ring_order);
> > +	int32_t error;
> > +
> > +	cons = intf->out_cons;
> > +	prod = intf->out_prod;
> > +	error = intf->out_error;
> > +	/* read indexes before continuing */
> > +	virt_mb();
> > +
> > +	if (error < 0)
> > +		return error;
> > +
> > +	size = pvcalls_queued(prod, cons, array_size);
> > +	if (size >= array_size)
> > +		return 0;
> > +	if (len > array_size - size)
> > +		len = array_size - size;
> > +
> > +	masked_prod = pvcalls_mask(prod, array_size);
> > +	masked_cons = pvcalls_mask(cons, array_size);
> > +
> > +	if (masked_prod < masked_cons) {
> > +		copy_from_iter(data->out + masked_prod, len, msg_iter);
> > +	} else {
> > +		if (len > array_size - masked_prod) {
> > +			copy_from_iter(data->out + masked_prod,
> > +				       array_size - masked_prod, msg_iter);
> > +			copy_from_iter(data->out,
> > +				       len - (array_size - masked_prod),
> > +				       msg_iter);
> > +		} else {
> > +			copy_from_iter(data->out + masked_prod, len, msg_iter);
> > +		}
> > +	}
> > +	/* write to ring before updating pointer */
> > +	virt_wmb();
> > +	intf->out_prod += len;
> > +
> > +	return len;
> > +}
> > +
> > +int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
> > +			  size_t len)
> > +{
> > +	struct pvcalls_bedata *bedata;
> > +	struct sock_mapping *map;
> > +	int sent = 0, tot_sent = 0;
> > +	int count = 0, flags;
> > +
> > +	if (!pvcalls_front_dev)
> > +		return -ENOTCONN;
> > +	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > +
> > +	map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> > +	if (!map)
> > +		return -ENOTSOCK;
> > +
> > +	flags = msg->msg_flags;
> > +	if (flags & (MSG_CONFIRM|MSG_DONTROUTE|MSG_EOR|MSG_OOB))
> > +		return -EOPNOTSUPP;
> > +
> > +	mutex_lock(&map->active.out_mutex);
> > +	if ((flags & MSG_DONTWAIT) && !pvcalls_front_write_todo(map)) {
> > +		mutex_unlock(&map->active.out_mutex);
> > +		return -EAGAIN;
> > +	}
> > +
> > +again:
> > +	count++;
> > +	sent = __write_ring(map->active.ring,
> > +			    &map->active.data, &msg->msg_iter,
> > +			    len);
> > +	if (sent > 0) {
> > +		len -= sent;
> > +		tot_sent += sent;
> > +		notify_remote_via_irq(map->active.irq);
> > +	}
> > +	if (sent >= 0 && len > 0 && count < PVCALLS_FRON_MAX_SPIN)
> > +		goto again;
> > +	if (sent < 0)
> > +		tot_sent = sent;
> > +
> > +	mutex_unlock(&map->active.out_mutex);
> > +	return tot_sent;
> > +}
> > +
> >  int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
> >  {
> >  	struct pvcalls_bedata *bedata;
> > diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
> > index ab4f1da..d937c24 100644
> > --- a/drivers/xen/pvcalls-front.h
> > +++ b/drivers/xen/pvcalls-front.h
> > @@ -13,5 +13,8 @@ int pvcalls_front_bind(struct socket *sock,
> >  int pvcalls_front_accept(struct socket *sock,
> >  			 struct socket *newsock,
> >  			 int flags);
> > +int pvcalls_front_sendmsg(struct socket *sock,
> > +			  struct msghdr *msg,
> > +			  size_t len);
> >  
> >  #endif
> > 
>