[PATCH 1/1 net-next] virtio_net: remove send queue

[PATCH 1/1 net-next] virtio_net: remove send queue

[Shirley Ma]

Use detach buffers API in virtio to free unused buffers in send queue when shutting down 
virtio_net to avoid maintaining skb link list for each transmit packet.

Signed-off-by: Shirley Ma <xma@us.ibm.com>
---
 drivers/net/virtio_net.c |   26 ++++++++------------------
 1 files changed, 8 insertions(+), 18 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9d8984a..8069c08 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -56,9 +56,6 @@ struct virtnet_info
 	/* Host will merge rx buffers for big packets (shake it! shake it!) */
 	bool mergeable_rx_bufs;
 
-	/* Send queue. */
-	struct sk_buff_head send;
-
 	/* Work struct for refilling if we run low on memory. */
 	struct delayed_work refill;
 
@@ -505,7 +502,6 @@ static unsigned int free_old_xmit_skbs(struct virtnet_info *vi)
 
 	while ((skb = vi->svq->vq_ops->get_buf(vi->svq, &len)) != NULL) {
 		pr_debug("Sent skb %p\n", skb);
-		__skb_unlink(skb, &vi->send);
 		vi->dev->stats.tx_bytes += skb->len;
 		vi->dev->stats.tx_packets++;
 		tot_sgs += skb_vnet_hdr(skb)->num_sg;
@@ -588,15 +584,6 @@ again:
 	}
 	vi->svq->vq_ops->kick(vi->svq);
 
-	/*
-	 * Put new one in send queue.  You'd expect we'd need this before
-	 * xmit_skb calls add_buf(), since the callback can be triggered
-	 * immediately after that.  But since the callback just triggers
-	 * another call back here, normal network xmit locking prevents the
-	 * race.
-	 */
-	__skb_queue_head(&vi->send, skb);
-
 	/* Don't wait up for transmitted skbs to be freed. */
 	skb_orphan(skb);
 	nf_reset(skb);
@@ -977,9 +964,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 			dev->features |= NETIF_F_HW_VLAN_FILTER;
 	}
 
-	/* Initialize our empty send queue. */
-	skb_queue_head_init(&vi->send);
-
 	err = register_netdev(dev);
 	if (err) {
 		pr_debug("virtio_net: registering device failed\n");
@@ -1016,6 +1000,12 @@ static void free_unused_bufs(struct virtnet_info *vi)
 {
 	void *buf;
 	while (1) {
+		buf = vi->svq->vq_ops->detach_unused_buf(vi->svq);
+		if (!buf)
+			break;
+		dev_kfree_skb(buf);
+	}
+	while (1) {
 		buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
 		if (!buf)
 			break;
@@ -1035,11 +1025,11 @@ static void __devexit virtnet_remove(struct virtio_device *vdev)
 	/* Stop all the virtqueues. */
 	vdev->config->reset(vdev);
 
-	/* Free our skbs in send queue, if any. */
-	__skb_queue_purge(&vi->send);
 
 	unregister_netdev(vi->dev);
 	cancel_delayed_work_sync(&vi->refill);
+
+	/* Free unused buffers in both send and recv, if any. */
 	free_unused_bufs(vi);
 
 	vdev->config->del_vqs(vi->vdev);

[PATCH 0/1 net-next] virtio_net: remove send queue

[Shirley Ma]

This patch is built on top of net-next + defer skb patch for virtio_net.
The patch has been tested and some performance has been gained by
removing skb link & unlink for each packet in send queue.

thanks
Shirley

Re: [PATCH 1/1 net-next] virtio_net: remove send queue

[Michael S. Tsirkin]

On Tue, Feb 02, 2010 at 01:48:51PM -0800, Shirley Ma wrote:
> Use detach buffers API in virtio to free unused buffers in send queue when shutting down 
> virtio_net to avoid maintaining skb link list for each transmit packet.
> 
> Signed-off-by: Shirley Ma <xma@us.ibm.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/net/virtio_net.c |   26 ++++++++------------------
>  1 files changed, 8 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9d8984a..8069c08 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -56,9 +56,6 @@ struct virtnet_info
>  	/* Host will merge rx buffers for big packets (shake it! shake it!) */
>  	bool mergeable_rx_bufs;
>  
> -	/* Send queue. */
> -	struct sk_buff_head send;
> -
>  	/* Work struct for refilling if we run low on memory. */
>  	struct delayed_work refill;
>  
> @@ -505,7 +502,6 @@ static unsigned int free_old_xmit_skbs(struct virtnet_info *vi)
>  
>  	while ((skb = vi->svq->vq_ops->get_buf(vi->svq, &len)) != NULL) {
>  		pr_debug("Sent skb %p\n", skb);
> -		__skb_unlink(skb, &vi->send);
>  		vi->dev->stats.tx_bytes += skb->len;
>  		vi->dev->stats.tx_packets++;
>  		tot_sgs += skb_vnet_hdr(skb)->num_sg;
> @@ -588,15 +584,6 @@ again:
>  	}
>  	vi->svq->vq_ops->kick(vi->svq);
>  
> -	/*
> -	 * Put new one in send queue.  You'd expect we'd need this before
> -	 * xmit_skb calls add_buf(), since the callback can be triggered
> -	 * immediately after that.  But since the callback just triggers
> -	 * another call back here, normal network xmit locking prevents the
> -	 * race.
> -	 */
> -	__skb_queue_head(&vi->send, skb);
> -
>  	/* Don't wait up for transmitted skbs to be freed. */
>  	skb_orphan(skb);
>  	nf_reset(skb);
> @@ -977,9 +964,6 @@ static int virtnet_probe(struct virtio_device *vdev)
>  			dev->features |= NETIF_F_HW_VLAN_FILTER;
>  	}
>  
> -	/* Initialize our empty send queue. */
> -	skb_queue_head_init(&vi->send);
> -
>  	err = register_netdev(dev);
>  	if (err) {
>  		pr_debug("virtio_net: registering device failed\n");
> @@ -1016,6 +1000,12 @@ static void free_unused_bufs(struct virtnet_info *vi)
>  {
>  	void *buf;
>  	while (1) {
> +		buf = vi->svq->vq_ops->detach_unused_buf(vi->svq);
> +		if (!buf)
> +			break;
> +		dev_kfree_skb(buf);
> +	}
> +	while (1) {
>  		buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
>  		if (!buf)
>  			break;
> @@ -1035,11 +1025,11 @@ static void __devexit virtnet_remove(struct virtio_device *vdev)
>  	/* Stop all the virtqueues. */
>  	vdev->config->reset(vdev);
>  
> -	/* Free our skbs in send queue, if any. */
> -	__skb_queue_purge(&vi->send);
>  
>  	unregister_netdev(vi->dev);
>  	cancel_delayed_work_sync(&vi->refill);
> +
> +	/* Free unused buffers in both send and recv, if any. */
>  	free_unused_bufs(vi);
>  
>  	vdev->config->del_vqs(vi->vdev);
> 
> 
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Re: [PATCH 1/1 net-next] virtio_net: remove send queue

[Rusty Russell]

On Wed, 3 Feb 2010 08:18:51 am Shirley Ma wrote:
> Use detach buffers API in virtio to free unused buffers in send queue when shutting down 
> virtio_net to avoid maintaining skb link list for each transmit packet.
> 
> Signed-off-by: Shirley Ma <xma@us.ibm.com>

Hi Shirley,

  Nice cleanup.  Please cc: netdev@vger.kernel.org for net patches...

Your comment could be slightly enhanced to indicate that the API is new, eg;

	Now we have a virtio detach API (in commit XXXXXXXXXX), we don't need to
	track xmit skbs in the	driver.

Acked-by: Rusty Russell <rusty@rustcorp.com.au>

Thanks!
Rusty.