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[RFC,1/4] vsock/virtio: reduce credit update messages

Message ID 20190404105838.101559-2-sgarzare@redhat.com (mailing list archive)
State New, archived
Headers show
Series vsock/virtio: optimizations to increase the throughput | expand

Commit Message

Stefano Garzarella April 4, 2019, 10:58 a.m. UTC 
In order to reduce the number of credit update messages,
we send them only when the space available seen by the
transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 include/linux/virtio_vsock.h            |  1 +
 net/vmw_vsock/virtio_transport_common.c | 14 +++++++++++---
 2 files changed, 12 insertions(+), 3 deletions(-)

Comments

Stefan Hajnoczi April 4, 2019, 7:15 p.m. UTC | #1 
On Thu, Apr 04, 2019 at 12:58:35PM +0200, Stefano Garzarella wrote:
> @@ -256,6 +257,7 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
>  	struct virtio_vsock_sock *vvs = vsk->trans;
>  	struct virtio_vsock_pkt *pkt;
>  	size_t bytes, total = 0;
> +	s64 free_space;

Why s64?  buf_alloc, fwd_cnt, and last_fwd_cnt are all u32.  fwd_cnt -
last_fwd_cnt <= buf_alloc is always true.

>  	int err = -EFAULT;
>  
>  	spin_lock_bh(&vvs->rx_lock);
> @@ -288,9 +290,15 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
>  	}
>  	spin_unlock_bh(&vvs->rx_lock);
>  
> -	/* Send a credit pkt to peer */
> -	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM,
> -					    NULL);
> +	/* We send a credit update only when the space available seen
> +	 * by the transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE
> +	 */
> +	free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);

Locking?  These fields should be accessed under tx_lock.

> +	if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
> +		virtio_transport_send_credit_update(vsk,
> +						    VIRTIO_VSOCK_TYPE_STREAM,
> +						    NULL);
> +	}
Stefano Garzarella April 5, 2019, 8:16 a.m. UTC | #2 
On Thu, Apr 04, 2019 at 08:15:39PM +0100, Stefan Hajnoczi wrote:
> On Thu, Apr 04, 2019 at 12:58:35PM +0200, Stefano Garzarella wrote:
> > @@ -256,6 +257,7 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> >  	struct virtio_vsock_sock *vvs = vsk->trans;
> >  	struct virtio_vsock_pkt *pkt;
> >  	size_t bytes, total = 0;
> > +	s64 free_space;
> 
> Why s64?  buf_alloc, fwd_cnt, and last_fwd_cnt are all u32.  fwd_cnt -
> last_fwd_cnt <= buf_alloc is always true.
> 

Right, I'll use a u32 for free_space!
Is is a leftover because initially I implemented something like
virtio_transport_has_space().

> >  	int err = -EFAULT;
> >  
> >  	spin_lock_bh(&vvs->rx_lock);
> > @@ -288,9 +290,15 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> >  	}
> >  	spin_unlock_bh(&vvs->rx_lock);
> >  
> > -	/* Send a credit pkt to peer */
> > -	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM,
> > -					    NULL);
> > +	/* We send a credit update only when the space available seen
> > +	 * by the transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE
> > +	 */
> > +	free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
> 
> Locking?  These fields should be accessed under tx_lock.
> 

Yes, we need a lock, but looking in the code, vvs->fwd_cnd is written
taking rx_lock (virtio_transport_dec_rx_pkt) and it is read with the
tx_lock (virtio_transport_inc_tx_pkt).

Maybe we should use another spin_lock shared between RX and TX for those
fields or use atomic variables.

What do you suggest?

Thanks,
Stefano
Stefan Hajnoczi April 8, 2019, 9:25 a.m. UTC | #3 
On Fri, Apr 05, 2019 at 10:16:48AM +0200, Stefano Garzarella wrote:
> On Thu, Apr 04, 2019 at 08:15:39PM +0100, Stefan Hajnoczi wrote:
> > On Thu, Apr 04, 2019 at 12:58:35PM +0200, Stefano Garzarella wrote:
> > >  	int err = -EFAULT;
> > >  
> > >  	spin_lock_bh(&vvs->rx_lock);
> > > @@ -288,9 +290,15 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> > >  	}
> > >  	spin_unlock_bh(&vvs->rx_lock);
> > >  
> > > -	/* Send a credit pkt to peer */
> > > -	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM,
> > > -					    NULL);
> > > +	/* We send a credit update only when the space available seen
> > > +	 * by the transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE
> > > +	 */
> > > +	free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
> > 
> > Locking?  These fields should be accessed under tx_lock.
> > 
> 
> Yes, we need a lock, but looking in the code, vvs->fwd_cnd is written
> taking rx_lock (virtio_transport_dec_rx_pkt) and it is read with the
> tx_lock (virtio_transport_inc_tx_pkt).
> 
> Maybe we should use another spin_lock shared between RX and TX for those
> fields or use atomic variables.
> 
> What do you suggest?

Or make vvs->fwd_cnt atomic if it's the only field that needs to be
accessed in this manner.

Stefan
diff mbox series

Patch

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index e223e2632edd..6d7a22cc20bf 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -37,6 +37,7 @@  struct virtio_vsock_sock {
 	u32 tx_cnt;
 	u32 buf_alloc;
 	u32 peer_fwd_cnt;
+	u32 last_fwd_cnt;
 	u32 peer_buf_alloc;
 
 	/* Protected by rx_lock */
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 602715fc9a75..f32301d823f5 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -206,6 +206,7 @@  static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
 void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
 {
 	spin_lock_bh(&vvs->tx_lock);
+	vvs->last_fwd_cnt = vvs->fwd_cnt;
 	pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
 	pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc);
 	spin_unlock_bh(&vvs->tx_lock);
@@ -256,6 +257,7 @@  virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	struct virtio_vsock_sock *vvs = vsk->trans;
 	struct virtio_vsock_pkt *pkt;
 	size_t bytes, total = 0;
+	s64 free_space;
 	int err = -EFAULT;
 
 	spin_lock_bh(&vvs->rx_lock);
@@ -288,9 +290,15 @@  virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	}
 	spin_unlock_bh(&vvs->rx_lock);
 
-	/* Send a credit pkt to peer */
-	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM,
-					    NULL);
+	/* We send a credit update only when the space available seen
+	 * by the transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE
+	 */
+	free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
+	if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
+		virtio_transport_send_credit_update(vsk,
+						    VIRTIO_VSOCK_TYPE_STREAM,
+						    NULL);
+	}
 
 	return total;