[PATCH net-next 0/2] Defer skb allocation in virtio_net recv

[PATCH net-next 0/2] Defer skb allocation in virtio_net recv

[Shirley Ma]

This patch-set has deferred virtio_net skb allocation in receiving path
for both big packets and mergeable buffers. It reduces skb
pre-allocations and skb frees. This patch-set also add a new API
detach_unused_bufs in virtio. Recv skb queue has been removed in
virtio_net. It is based on previous Rusty and Michaels' review, patch
has split into two:

[PATCH 1/2] virtio: Add detach unused buffer from vring
[PATCH 2/2] virtio_net: Defer skb allocation in receive path

I copied Rusty's comment as [PATCH 1/2] commit message.

This patch is built against Dave's net-next tree.

Thanks
Shirley

 

[PATCH 1/2] virtio: Add detach unused buffer from vring

[Shirley Ma]

There's currently no way for a virtio driver to ask for unused
buffers, so it has to keep a list itself to reclaim them at shutdown.
This is redundant, since virtio_ring stores that information.  So
add a new hook to do this: virtio_net will be the first user.

Signed-off-by: Shirley Ma <xma@us.ibm.com>
--- 
 drivers/virtio/virtio_ring.c |   25 +++++++++++++++++++++++++
 include/linux/virtio.h       |    4 ++++
 2 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index fbd2ecd..71929ee 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -334,6 +334,30 @@ static bool vring_enable_cb(struct virtqueue *_vq)
 	return true;
 }
 
+static void *vring_detach_unused_buf(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	unsigned int i;
+	void *buf;
+
+	START_USE(vq);
+
+	for (i = 0; i < vq->vring.num; i++) {
+		if (!vq->data[i])
+			continue;
+		/* detach_buf clears data, so grab it now. */
+		buf = vq->data[i];
+		detach_buf(vq, i);
+		END_USE(vq);
+		return buf;
+	}
+	/* That should have freed everything. */
+	BUG_ON(vq->num_free != vq->vring.num);
+
+	END_USE(vq);
+	return NULL;
+}
+
 irqreturn_t vring_interrupt(int irq, void *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
@@ -360,6 +384,7 @@ static struct virtqueue_ops vring_vq_ops = {
 	.kick = vring_kick,
 	.disable_cb = vring_disable_cb,
 	.enable_cb = vring_enable_cb,
+	.detach_unused_buf = vring_detach_unused_buf,
 };
 
 struct virtqueue *vring_new_virtqueue(unsigned int num,
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 057a2e0..f508c65 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -51,6 +51,9 @@ struct virtqueue {
  *	This re-enables callbacks; it returns "false" if there are pending
  *	buffers in the queue, to detect a possible race between the driver
  *	checking for more work, and enabling callbacks.
+ * @detach_unused_buf: detach first unused buffer
+ * 	vq: the struct virtqueue we're talking about.
+ * 	Returns NULL or the "data" token handed to add_buf
  *
  * Locking rules are straightforward: the driver is responsible for
  * locking.  No two operations may be invoked simultaneously, with the exception
@@ -71,6 +74,7 @@ struct virtqueue_ops {
 
 	void (*disable_cb)(struct virtqueue *vq);
 	bool (*enable_cb)(struct virtqueue *vq);
+	void *(*detach_unused_buf)(struct virtqueue *vq);
 };
 
 /**

[PATCH 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

virtio_net receives packets from its pre-allocated vring buffers, then it 
delivers these packets to upper layer protocols as skb buffs. So it's not
necessary to pre-allocate skb for each mergable buffer, then frees extra 
skbs when buffers are merged into a large packet. This patch has deferred 
skb allocation in receiving packets for both big packets and mergeable buffers
to reduce skb pre-allocations and skb frees. It frees unused buffers by calling 
detach_unused_buf in vring, so recv skb queue is not needed.

Signed-off-by: Shirley Ma <xma@us.ibm.com>
---
 drivers/net/virtio_net.c |  426 +++++++++++++++++++++++++++-------------------
 1 files changed, 247 insertions(+), 179 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c708ecc..bb57b96 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -56,8 +56,7 @@ struct virtnet_info
 	/* Host will merge rx buffers for big packets (shake it! shake it!) */
 	bool mergeable_rx_bufs;
 
-	/* Receive & send queues. */
-	struct sk_buff_head recv;
+	/* Send queue. */
 	struct sk_buff_head send;
 
 	/* Work struct for refilling if we run low on memory. */
@@ -75,34 +74,44 @@ struct skb_vnet_hdr {
 	unsigned int num_sg;
 };
 
+struct padded_vnet_hdr {
+	struct virtio_net_hdr hdr;
+	/*
+	 * virtio_net_hdr should be in a separated sg buffer because of a
+	 * QEMU bug, and data sg buffer shares same page with this header sg.
+	 * This padding makes next sg 16 byte aligned after virtio_net_hdr.
+	 */
+	char padding[6];
+};
+
 static inline struct skb_vnet_hdr *skb_vnet_hdr(struct sk_buff *skb)
 {
 	return (struct skb_vnet_hdr *)skb->cb;
 }
 
-static void give_a_page(struct virtnet_info *vi, struct page *page)
-{
-	page->private = (unsigned long)vi->pages;
-	vi->pages = page;
-}
-
-static void trim_pages(struct virtnet_info *vi, struct sk_buff *skb)
+/*
+ * private is used to chain pages for big packets, put the whole
+ * most recent used list in the beginning for reuse
+ */
+static void give_pages(struct virtnet_info *vi, struct page *page)
 {
-	unsigned int i;
+	struct page *end;
 
-	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
-		give_a_page(vi, skb_shinfo(skb)->frags[i].page);
-	skb_shinfo(skb)->nr_frags = 0;
-	skb->data_len = 0;
+	/* Find end of list, sew whole thing into vi->pages. */
+	for (end = page; end->private; end = (struct page *)end->private);
+	end->private = (unsigned long)vi->pages;
+	vi->pages = page;
 }
 
 static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
 {
 	struct page *p = vi->pages;
 
-	if (p)
+	if (p) {
 		vi->pages = (struct page *)p->private;
-	else
+		/* clear private here, it is used to chain pages */
+		p->private = 0;
+	} else
 		p = alloc_page(gfp_mask);
 	return p;
 }
@@ -118,99 +127,142 @@ static void skb_xmit_done(struct virtqueue *svq)
 	netif_wake_queue(vi->dev);
 }
 
-static void receive_skb(struct net_device *dev, struct sk_buff *skb,
-			unsigned len)
+static void set_skb_frag(struct sk_buff *skb, struct page *page,
+			 unsigned int offset, unsigned int *len)
 {
-	struct virtnet_info *vi = netdev_priv(dev);
-	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
-	int err;
-	int i;
+	int i = skb_shinfo(skb)->nr_frags;
+	skb_frag_t *f;
+
+	f = &skb_shinfo(skb)->frags[i];
+	f->size = min((unsigned)PAGE_SIZE - offset, *len);
+	f->page_offset = offset;
+	f->page = page;
+
+	skb->data_len += f->size;
+	skb->len += f->size;
+	skb_shinfo(skb)->nr_frags++;
+	*len -= f->size;
+}
 
-	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
-		pr_debug("%s: short packet %i\n", dev->name, len);
-		dev->stats.rx_length_errors++;
-		goto drop;
-	}
+static struct sk_buff *page_to_skb(struct virtnet_info *vi,
+				   struct page *page, unsigned int len)
+{
+	struct sk_buff *skb;
+	struct skb_vnet_hdr *hdr;
+	unsigned int copy, hdr_len, offset;
+	char *p;
 
-	if (vi->mergeable_rx_bufs) {
-		unsigned int copy;
-		char *p = page_address(skb_shinfo(skb)->frags[0].page);
+	p = page_address(page);
 
-		if (len > PAGE_SIZE)
-			len = PAGE_SIZE;
-		len -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
+	/* copy small packet so we can reuse these pages for small data */
+	skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
+	if (unlikely(!skb))
+		return NULL;
 
-		memcpy(&hdr->mhdr, p, sizeof(hdr->mhdr));
-		p += sizeof(hdr->mhdr);
+	hdr = skb_vnet_hdr(skb);
 
-		copy = len;
-		if (copy > skb_tailroom(skb))
-			copy = skb_tailroom(skb);
+	if (vi->mergeable_rx_bufs) {
+		hdr_len = sizeof hdr->mhdr;
+		offset = hdr_len;
+	} else {
+		hdr_len = sizeof hdr->hdr;
+		offset = sizeof(struct padded_vnet_hdr);
+	}
 
-		memcpy(skb_put(skb, copy), p, copy);
+	memcpy(hdr, p, hdr_len);
 
-		len -= copy;
+	len -= hdr_len;
+	p += offset;
 
-		if (!len) {
-			give_a_page(vi, skb_shinfo(skb)->frags[0].page);
-			skb_shinfo(skb)->nr_frags--;
-		} else {
-			skb_shinfo(skb)->frags[0].page_offset +=
-				sizeof(hdr->mhdr) + copy;
-			skb_shinfo(skb)->frags[0].size = len;
-			skb->data_len += len;
-			skb->len += len;
-		}
+	copy = len;
+	if (copy > skb_tailroom(skb))
+		copy = skb_tailroom(skb);
+	memcpy(skb_put(skb, copy), p, copy);
 
-		while (--hdr->mhdr.num_buffers) {
-			struct sk_buff *nskb;
+	len -= copy;
+	offset += copy;
 
-			i = skb_shinfo(skb)->nr_frags;
-			if (i >= MAX_SKB_FRAGS) {
-				pr_debug("%s: packet too long %d\n", dev->name,
-					 len);
-				dev->stats.rx_length_errors++;
-				goto drop;
-			}
-
-			nskb = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
-			if (!nskb) {
-				pr_debug("%s: rx error: %d buffers missing\n",
-					 dev->name, hdr->mhdr.num_buffers);
-				dev->stats.rx_length_errors++;
-				goto drop;
-			}
+	while (len) {
+		set_skb_frag(skb, page, offset, &len);
+		page = (struct page *)page->private;
+		offset = 0;
+	}
 
-			__skb_unlink(nskb, &vi->recv);
-			vi->num--;
+	if (page)
+		give_pages(vi, page);
 
-			skb_shinfo(skb)->frags[i] = skb_shinfo(nskb)->frags[0];
-			skb_shinfo(nskb)->nr_frags = 0;
-			kfree_skb(nskb);
+	return skb;
+}
 
-			if (len > PAGE_SIZE)
-				len = PAGE_SIZE;
+static int receive_mergeable(struct virtnet_info *vi, struct sk_buff *skb)
+{
+	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
+	struct page *page;
+	int num_buf, i, len;
+
+	num_buf = hdr->mhdr.num_buffers;
+	while (--num_buf) {
+		i = skb_shinfo(skb)->nr_frags;
+		if (i >= MAX_SKB_FRAGS) {
+			pr_debug("%s: packet too long\n", skb->dev->name);
+			skb->dev->stats.rx_length_errors++;
+			return -EINVAL;
+		}
 
-			skb_shinfo(skb)->frags[i].size = len;
-			skb_shinfo(skb)->nr_frags++;
-			skb->data_len += len;
-			skb->len += len;
+		page = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
+		if (!page) {
+			pr_debug("%s: rx error: %d buffers missing\n",
+				 skb->dev->name, hdr->mhdr.num_buffers);
+			skb->dev->stats.rx_length_errors++;
+			return -EINVAL;
 		}
-	} else {
-		len -= sizeof(hdr->hdr);
+		if (len > PAGE_SIZE)
+			len = PAGE_SIZE;
 
-		if (len <= MAX_PACKET_LEN)
-			trim_pages(vi, skb);
+		set_skb_frag(skb, page, 0, &len);
+
+		--vi->num;
+	}
+	return 0;
+}
 
-		err = pskb_trim(skb, len);
-		if (err) {
-			pr_debug("%s: pskb_trim failed %i %d\n", dev->name,
-				 len, err);
+static void receive_buf(struct net_device *dev, void *buf, unsigned int len)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	struct sk_buff *skb;
+	struct page *page;
+	struct skb_vnet_hdr *hdr;
+
+	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
+		pr_debug("%s: short packet %i\n", dev->name, len);
+		dev->stats.rx_length_errors++;
+		if (vi->mergeable_rx_bufs || vi->big_packets)
+			give_pages(vi, buf);
+		else
+			dev_kfree_skb(buf);
+		return;
+	}
+
+	if (!vi->mergeable_rx_bufs && !vi->big_packets) {
+		skb = buf;
+		len -= sizeof(struct virtio_net_hdr);
+		skb_trim(skb, len);
+	} else {
+		page = buf;
+		skb = page_to_skb(vi, page, len);
+		if (unlikely(!skb)) {
 			dev->stats.rx_dropped++;
-			goto drop;
+			give_pages(vi, page);
+			return;
 		}
+		if (vi->mergeable_rx_bufs)
+			if (receive_mergeable(vi, skb)) {
+				dev_kfree_skb(skb);
+				return;
+			}
 	}
 
+	hdr = skb_vnet_hdr(skb);
 	skb->truesize += skb->data_len;
 	dev->stats.rx_bytes += skb->len;
 	dev->stats.rx_packets++;
@@ -267,110 +319,119 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb,
 
 frame_err:
 	dev->stats.rx_frame_errors++;
-drop:
 	dev_kfree_skb(skb);
 }
 
-static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
+static int add_recvbuf_small(struct virtnet_info *vi, gfp_t gfp)
 {
 	struct sk_buff *skb;
-	struct scatterlist sg[2+MAX_SKB_FRAGS];
-	int num, err, i;
-	bool oom = false;
-
-	sg_init_table(sg, 2+MAX_SKB_FRAGS);
-	do {
-		struct skb_vnet_hdr *hdr;
+	struct skb_vnet_hdr *hdr;
+	struct scatterlist sg[2];
+	int err;
 
-		skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
-		if (unlikely(!skb)) {
-			oom = true;
-			break;
-		}
+	skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
+	if (unlikely(!skb))
+		return -ENOMEM;
 
-		skb_put(skb, MAX_PACKET_LEN);
+	skb_put(skb, MAX_PACKET_LEN);
 
-		hdr = skb_vnet_hdr(skb);
-		sg_set_buf(sg, &hdr->hdr, sizeof(hdr->hdr));
+	hdr = skb_vnet_hdr(skb);
+	sg_set_buf(sg, &hdr->hdr, sizeof hdr->hdr);
 
-		if (vi->big_packets) {
-			for (i = 0; i < MAX_SKB_FRAGS; i++) {
-				skb_frag_t *f = &skb_shinfo(skb)->frags[i];
-				f->page = get_a_page(vi, gfp);
-				if (!f->page)
-					break;
+	skb_to_sgvec(skb, sg + 1, 0, skb->len);
 
-				f->page_offset = 0;
-				f->size = PAGE_SIZE;
+	err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 2, skb);
+	if (err < 0)
+		dev_kfree_skb(skb);
 
-				skb->data_len += PAGE_SIZE;
-				skb->len += PAGE_SIZE;
+	return err;
+}
 
-				skb_shinfo(skb)->nr_frags++;
-			}
+static int add_recvbuf_big(struct virtnet_info *vi, gfp_t gfp)
+{
+	struct scatterlist sg[MAX_SKB_FRAGS + 2];
+	struct page *first, *list = NULL;
+	char *p;
+	int i, err, offset;
+
+	/* page in sg[MAX_SKB_FRAGS + 1] is list tail */
+	for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
+		first = get_a_page(vi, gfp);
+		if (!first) {
+			if (list)
+				give_pages(vi, list);
+			return -ENOMEM;
 		}
+		sg_set_buf(&sg[i], page_address(first), PAGE_SIZE);
 
-		num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
-		skb_queue_head(&vi->recv, skb);
+		/* chain new page in list head to match sg */
+		first->private = (unsigned long)list;
+		list = first;
+	}
 
-		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
-		if (err < 0) {
-			skb_unlink(skb, &vi->recv);
-			trim_pages(vi, skb);
-			kfree_skb(skb);
-			break;
-		}
-		vi->num++;
-	} while (err >= num);
-	if (unlikely(vi->num > vi->max))
-		vi->max = vi->num;
-	vi->rvq->vq_ops->kick(vi->rvq);
-	return !oom;
+	first = get_a_page(vi, gfp);
+	if (!first) {
+		give_pages(vi, list);
+		return -ENOMEM;
+	}
+	p = page_address(first);
+
+	/* sg[0], sg[1] share the same page */
+	/* a separated sg[0] for  virtio_net_hdr only during to QEMU bug*/
+	sg_set_buf(&sg[0], p, sizeof(struct virtio_net_hdr));
+
+	/* sg[1] for data packet, from offset */
+	offset = sizeof(struct padded_vnet_hdr);
+	sg_set_buf(&sg[1], p + offset, PAGE_SIZE - offset);
+
+	/* chain first in list head */
+	first->private = (unsigned long)list;
+	err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, MAX_SKB_FRAGS + 2,
+				       first);
+	if (err < 0)
+		give_pages(vi, first);
+
+	return err;
 }
 
-/* Returns false if we couldn't fill entirely (OOM). */
-static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
+static int add_recvbuf_mergeable(struct virtnet_info *vi, gfp_t gfp)
 {
-	struct sk_buff *skb;
-	struct scatterlist sg[1];
+	struct page *page;
+	struct scatterlist sg;
 	int err;
-	bool oom = false;
-
-	if (!vi->mergeable_rx_bufs)
-		return try_fill_recv_maxbufs(vi, gfp);
 
-	do {
-		skb_frag_t *f;
+	page = get_a_page(vi, gfp);
+	if (!page)
+		return -ENOMEM;
 
-		skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
-		if (unlikely(!skb)) {
-			oom = true;
-			break;
-		}
+	sg_init_one(&sg, page_address(page), PAGE_SIZE);
 
-		f = &skb_shinfo(skb)->frags[0];
-		f->page = get_a_page(vi, gfp);
-		if (!f->page) {
-			oom = true;
-			kfree_skb(skb);
-			break;
-		}
+	err = vi->rvq->vq_ops->add_buf(vi->rvq, &sg, 0, 1, page);
+	if (err < 0)
+		give_pages(vi, page);
 
-		f->page_offset = 0;
-		f->size = PAGE_SIZE;
+	return err;
+}
 
-		skb_shinfo(skb)->nr_frags++;
+/* Returns false if we couldn't fill entirely (OOM). */
+static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
+{
+	int err;
+	bool oom = false;
 
-		sg_init_one(sg, page_address(f->page), PAGE_SIZE);
-		skb_queue_head(&vi->recv, skb);
+	do {
+		if (vi->mergeable_rx_bufs)
+			err = add_recvbuf_mergeable(vi, gfp);
+		else if (vi->big_packets)
+			err = add_recvbuf_big(vi, gfp);
+		else
+			err = add_recvbuf_small(vi, gfp);
 
-		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
 		if (err < 0) {
-			skb_unlink(skb, &vi->recv);
-			kfree_skb(skb);
+			oom = true;
 			break;
 		}
-		vi->num++;
+		++vi->num;
 	} while (err > 0);
 	if (unlikely(vi->num > vi->max))
 		vi->max = vi->num;
@@ -408,15 +469,14 @@ static void refill_work(struct work_struct *work)
 static int virtnet_poll(struct napi_struct *napi, int budget)
 {
 	struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi);
-	struct sk_buff *skb = NULL;
+	void *buf;
 	unsigned int len, received = 0;
 
 again:
 	while (received < budget &&
-	       (skb = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) {
-		__skb_unlink(skb, &vi->recv);
-		receive_skb(vi->dev, skb, len);
-		vi->num--;
+	       (buf = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) {
+		receive_buf(vi->dev, buf, len);
+		--vi->num;
 		received++;
 	}
 
@@ -496,9 +556,9 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
 
 	/* Encode metadata header at front. */
 	if (vi->mergeable_rx_bufs)
-		sg_set_buf(sg, &hdr->mhdr, sizeof(hdr->mhdr));
+		sg_set_buf(sg, &hdr->mhdr, sizeof hdr->mhdr);
 	else
-		sg_set_buf(sg, &hdr->hdr, sizeof(hdr->hdr));
+		sg_set_buf(sg, &hdr->hdr, sizeof hdr->hdr);
 
 	hdr->num_sg = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
 	return vi->svq->vq_ops->add_buf(vi->svq, sg, hdr->num_sg, 0, skb);
@@ -916,8 +976,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 			dev->features |= NETIF_F_HW_VLAN_FILTER;
 	}
 
-	/* Initialize our empty receive and send queues. */
-	skb_queue_head_init(&vi->recv);
+	/* Initialize our empty send queue. */
 	skb_queue_head_init(&vi->send);
 
 	err = register_netdev(dev);
@@ -952,25 +1011,34 @@ free:
 	return err;
 }
 
+static void free_unused_bufs(struct virtnet_info *vi)
+{
+	void *buf;
+	while (vi->num) {
+		buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
+		if (!buf)
+			continue;
+		if (vi->mergeable_rx_bufs || vi->big_packets)
+			give_pages(vi, buf);
+		else
+			dev_kfree_skb(buf);
+		--vi->num;
+	}
+}
+
 static void __devexit virtnet_remove(struct virtio_device *vdev)
 {
 	struct virtnet_info *vi = vdev->priv;
-	struct sk_buff *skb;
 
 	/* Stop all the virtqueues. */
 	vdev->config->reset(vdev);
 
-	/* Free our skbs in send and recv queues, if any. */
-	while ((skb = __skb_dequeue(&vi->recv)) != NULL) {
-		kfree_skb(skb);
-		vi->num--;
-	}
+	/* Free our skbs in send queue, if any. */
 	__skb_queue_purge(&vi->send);
 
-	BUG_ON(vi->num != 0);
-
 	unregister_netdev(vi->dev);
 	cancel_delayed_work_sync(&vi->refill);
+	free_unused_bufs(vi);
 
 	vdev->config->del_vqs(vi->vdev);
 

Re: [PATCH net-next 0/2] Defer skb allocation in virtio_net recv

[Shirley Ma]

Send skb queue can also be reduced with detach_unused_buf API by it is
not a part of this patch.

Shirley

Re: [PATCH 1/2] virtio: Add detach unused buffer from vring

[Michael S. Tsirkin]

On Thu, Dec 17, 2009 at 11:43:50PM -0800, Shirley Ma wrote:
> There's currently no way for a virtio driver to ask for unused
> buffers, so it has to keep a list itself to reclaim them at shutdown.
> This is redundant, since virtio_ring stores that information.  So
> add a new hook to do this: virtio_net will be the first user.
> 
> Signed-off-by: Shirley Ma <xma@us.ibm.com>

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

> --- 
>  drivers/virtio/virtio_ring.c |   25 +++++++++++++++++++++++++
>  include/linux/virtio.h       |    4 ++++
>  2 files changed, 29 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index fbd2ecd..71929ee 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -334,6 +334,30 @@ static bool vring_enable_cb(struct virtqueue *_vq)
>  	return true;
>  }
>  
> +static void *vring_detach_unused_buf(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	unsigned int i;
> +	void *buf;
> +
> +	START_USE(vq);
> +
> +	for (i = 0; i < vq->vring.num; i++) {
> +		if (!vq->data[i])
> +			continue;
> +		/* detach_buf clears data, so grab it now. */
> +		buf = vq->data[i];
> +		detach_buf(vq, i);
> +		END_USE(vq);
> +		return buf;
> +	}
> +	/* That should have freed everything. */
> +	BUG_ON(vq->num_free != vq->vring.num);
> +
> +	END_USE(vq);
> +	return NULL;
> +}
> +
>  irqreturn_t vring_interrupt(int irq, void *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> @@ -360,6 +384,7 @@ static struct virtqueue_ops vring_vq_ops = {
>  	.kick = vring_kick,
>  	.disable_cb = vring_disable_cb,
>  	.enable_cb = vring_enable_cb,
> +	.detach_unused_buf = vring_detach_unused_buf,
>  };
>  
>  struct virtqueue *vring_new_virtqueue(unsigned int num,
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 057a2e0..f508c65 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -51,6 +51,9 @@ struct virtqueue {
>   *	This re-enables callbacks; it returns "false" if there are pending
>   *	buffers in the queue, to detect a possible race between the driver
>   *	checking for more work, and enabling callbacks.
> + * @detach_unused_buf: detach first unused buffer
> + * 	vq: the struct virtqueue we're talking about.
> + * 	Returns NULL or the "data" token handed to add_buf
>   *
>   * Locking rules are straightforward: the driver is responsible for
>   * locking.  No two operations may be invoked simultaneously, with the exception
> @@ -71,6 +74,7 @@ struct virtqueue_ops {
>  
>  	void (*disable_cb)(struct virtqueue *vq);
>  	bool (*enable_cb)(struct virtqueue *vq);
> +	void *(*detach_unused_buf)(struct virtqueue *vq);
>  };
>  
>  /**
> 

Re: [PATCH 1/2] virtio: Add detach unused buffer from vring

[Amit Shah]

On (Thu) Dec 17 2009 [23:43:50], Shirley Ma wrote:
> There's currently no way for a virtio driver to ask for unused
> buffers, so it has to keep a list itself to reclaim them at shutdown.
> This is redundant, since virtio_ring stores that information.  So
> add a new hook to do this: virtio_net will be the first user.
> 
> Signed-off-by: Shirley Ma <xma@us.ibm.com>

Acked-By: Amit Shah <amit.shah@redhat.com>

		Amit

Re: [PATCH 2/2] virtio_net: Defer skb allocation in receive path

[Amit Shah]

On (Thu) Dec 17 2009 [23:44:49], Shirley Ma wrote:
> virtio_net receives packets from its pre-allocated vring buffers, then it 
> delivers these packets to upper layer protocols as skb buffs. So it's not
> necessary to pre-allocate skb for each mergable buffer, then frees extra 
> skbs when buffers are merged into a large packet. This patch has deferred 
> skb allocation in receiving packets for both big packets and mergeable buffers
> to reduce skb pre-allocations and skb frees. It frees unused buffers by calling 
> detach_unused_buf in vring, so recv skb queue is not needed.
> 
> Signed-off-by: Shirley Ma <xma@us.ibm.com>

...

> +static void free_unused_bufs(struct virtnet_info *vi)
> +{
> +	void *buf;
> +	while (vi->num) {
> +		buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
> +		if (!buf)
> +			continue;

Do you mean 'break' here?

> +		if (vi->mergeable_rx_bufs || vi->big_packets)
> +			give_pages(vi, buf);
> +		else
> +			dev_kfree_skb(buf);
> +		--vi->num;
> +	}
> +}
> +

		Amit

Re: [PATCH 2/2] virtio_net: Defer skb allocation in receive path

[Michael S. Tsirkin]

On Mon, Jan 04, 2010 at 01:25:44PM -0800, Shirley Ma wrote:
> Hello Amit,
> 
> Sorry for late response. I am just back from vacation.
> 
> On Thu, 2009-12-24 at 19:07 +0530, Amit Shah wrote:
> > > +static void free_unused_bufs(struct virtnet_info *vi)
> > > +{
> > > +     void *buf;
> > > +     while (vi->num) {
> > > +             buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
> > > +             if (!buf)
> > > +                     continue;
> > 
> > Do you mean 'break' here?
> 
> Nope, it means break since the buffer usage is not sorted by descriptors
> from my understanding. It breaks when vi->num reaches 0.
> 
> Thanks
> Shirley
t

I don't understand.
detach_unused_buf has:
+               if (!vq->data[i])
+                       continue;

so it will never return NULL unless no more buffers?  breaking here ad
BUG_ON(vi->num) as Amit suggests seems cleaner than looping forever if
there's a bug.

-- 
MST

Re: [PATCH 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

Hello Amit,

Sorry for late response. I am just back from vacation.

On Thu, 2009-12-24 at 19:07 +0530, Amit Shah wrote:
> > +static void free_unused_bufs(struct virtnet_info *vi)
> > +{
> > +     void *buf;
> > +     while (vi->num) {
> > +             buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
> > +             if (!buf)
> > +                     continue;
> 
> Do you mean 'break' here?

Nope, it means break since the buffer usage is not sorted by descriptors
from my understanding. It breaks when vi->num reaches 0.

Thanks
Shirley

Re: [PATCH 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

On Mon, 2010-01-04 at 23:14 +0200, Michael S. Tsirkin wrote:
> so it will never return NULL unless no more buffers?  breaking here ad
> BUG_ON(vi->num) as Amit suggests seems cleaner than looping forever if
> there's a bug. 

Agree. I will change to break as Amit suggested and put BUG_ON and
resubmit the patch.

Thanks
Shirley

[PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

virtio_net receives packets from its pre-allocated vring buffers, then it 
delivers these packets to upper layer protocols as skb buffs. So it's not
necessary to pre-allocate skb for each mergable buffer, then frees extra 
skbs when buffers are merged into a large packet. This patch has deferred 
skb allocation in receiving packets for both big packets and mergeable buffers
to reduce skb pre-allocations and skb frees. It frees unused buffers by calling 
detach_unused_buf in vring, so recv skb queue is not needed.

Signed-off-by: Shirley Ma <xma@us.ibm.com>
---
 drivers/net/virtio_net.c |  427 +++++++++++++++++++++++++++-------------------
 1 files changed, 248 insertions(+), 179 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c708ecc..72b3f21 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -56,8 +56,7 @@ struct virtnet_info
 	/* Host will merge rx buffers for big packets (shake it! shake it!) */
 	bool mergeable_rx_bufs;
 
-	/* Receive & send queues. */
-	struct sk_buff_head recv;
+	/* Send queue. */
 	struct sk_buff_head send;
 
 	/* Work struct for refilling if we run low on memory. */
@@ -75,34 +74,44 @@ struct skb_vnet_hdr {
 	unsigned int num_sg;
 };
 
+struct padded_vnet_hdr {
+	struct virtio_net_hdr hdr;
+	/*
+	 * virtio_net_hdr should be in a separated sg buffer because of a
+	 * QEMU bug, and data sg buffer shares same page with this header sg.
+	 * This padding makes next sg 16 byte aligned after virtio_net_hdr.
+	 */
+	char padding[6];
+};
+
 static inline struct skb_vnet_hdr *skb_vnet_hdr(struct sk_buff *skb)
 {
 	return (struct skb_vnet_hdr *)skb->cb;
 }
 
-static void give_a_page(struct virtnet_info *vi, struct page *page)
-{
-	page->private = (unsigned long)vi->pages;
-	vi->pages = page;
-}
-
-static void trim_pages(struct virtnet_info *vi, struct sk_buff *skb)
+/*
+ * private is used to chain pages for big packets, put the whole
+ * most recent used list in the beginning for reuse
+ */
+static void give_pages(struct virtnet_info *vi, struct page *page)
 {
-	unsigned int i;
+	struct page *end;
 
-	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
-		give_a_page(vi, skb_shinfo(skb)->frags[i].page);
-	skb_shinfo(skb)->nr_frags = 0;
-	skb->data_len = 0;
+	/* Find end of list, sew whole thing into vi->pages. */
+	for (end = page; end->private; end = (struct page *)end->private);
+	end->private = (unsigned long)vi->pages;
+	vi->pages = page;
 }
 
 static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
 {
 	struct page *p = vi->pages;
 
-	if (p)
+	if (p) {
 		vi->pages = (struct page *)p->private;
-	else
+		/* clear private here, it is used to chain pages */
+		p->private = 0;
+	} else
 		p = alloc_page(gfp_mask);
 	return p;
 }
@@ -118,99 +127,142 @@ static void skb_xmit_done(struct virtqueue *svq)
 	netif_wake_queue(vi->dev);
 }
 
-static void receive_skb(struct net_device *dev, struct sk_buff *skb,
-			unsigned len)
+static void set_skb_frag(struct sk_buff *skb, struct page *page,
+			 unsigned int offset, unsigned int *len)
 {
-	struct virtnet_info *vi = netdev_priv(dev);
-	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
-	int err;
-	int i;
-
-	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
-		pr_debug("%s: short packet %i\n", dev->name, len);
-		dev->stats.rx_length_errors++;
-		goto drop;
-	}
+	int i = skb_shinfo(skb)->nr_frags;
+	skb_frag_t *f;
+
+	f = &skb_shinfo(skb)->frags[i];
+	f->size = min((unsigned)PAGE_SIZE - offset, *len);
+	f->page_offset = offset;
+	f->page = page;
+
+	skb->data_len += f->size;
+	skb->len += f->size;
+	skb_shinfo(skb)->nr_frags++;
+	*len -= f->size;
+}
 
-	if (vi->mergeable_rx_bufs) {
-		unsigned int copy;
-		char *p = page_address(skb_shinfo(skb)->frags[0].page);
+static struct sk_buff *page_to_skb(struct virtnet_info *vi,
+				   struct page *page, unsigned int len)
+{
+	struct sk_buff *skb;
+	struct skb_vnet_hdr *hdr;
+	unsigned int copy, hdr_len, offset;
+	char *p;
 
-		if (len > PAGE_SIZE)
-			len = PAGE_SIZE;
-		len -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
+	p = page_address(page);
 
-		memcpy(&hdr->mhdr, p, sizeof(hdr->mhdr));
-		p += sizeof(hdr->mhdr);
+	/* copy small packet so we can reuse these pages for small data */
+	skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
+	if (unlikely(!skb))
+		return NULL;
 
-		copy = len;
-		if (copy > skb_tailroom(skb))
-			copy = skb_tailroom(skb);
+	hdr = skb_vnet_hdr(skb);
 
-		memcpy(skb_put(skb, copy), p, copy);
+	if (vi->mergeable_rx_bufs) {
+		hdr_len = sizeof hdr->mhdr;
+		offset = hdr_len;
+	} else {
+		hdr_len = sizeof hdr->hdr;
+		offset = sizeof(struct padded_vnet_hdr);
+	}
 
-		len -= copy;
+	memcpy(hdr, p, hdr_len);
 
-		if (!len) {
-			give_a_page(vi, skb_shinfo(skb)->frags[0].page);
-			skb_shinfo(skb)->nr_frags--;
-		} else {
-			skb_shinfo(skb)->frags[0].page_offset +=
-				sizeof(hdr->mhdr) + copy;
-			skb_shinfo(skb)->frags[0].size = len;
-			skb->data_len += len;
-			skb->len += len;
-		}
+	len -= hdr_len;
+	p += offset;
 
-		while (--hdr->mhdr.num_buffers) {
-			struct sk_buff *nskb;
+	copy = len;
+	if (copy > skb_tailroom(skb))
+		copy = skb_tailroom(skb);
+	memcpy(skb_put(skb, copy), p, copy);
 
-			i = skb_shinfo(skb)->nr_frags;
-			if (i >= MAX_SKB_FRAGS) {
-				pr_debug("%s: packet too long %d\n", dev->name,
-					 len);
-				dev->stats.rx_length_errors++;
-				goto drop;
-			}
+	len -= copy;
+	offset += copy;
 
-			nskb = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
-			if (!nskb) {
-				pr_debug("%s: rx error: %d buffers missing\n",
-					 dev->name, hdr->mhdr.num_buffers);
-				dev->stats.rx_length_errors++;
-				goto drop;
-			}
+	while (len) {
+		set_skb_frag(skb, page, offset, &len);
+		page = (struct page *)page->private;
+		offset = 0;
+	}
 
-			__skb_unlink(nskb, &vi->recv);
-			vi->num--;
+	if (page)
+		give_pages(vi, page);
 
-			skb_shinfo(skb)->frags[i] = skb_shinfo(nskb)->frags[0];
-			skb_shinfo(nskb)->nr_frags = 0;
-			kfree_skb(nskb);
+	return skb;
+}
 
-			if (len > PAGE_SIZE)
-				len = PAGE_SIZE;
+static int receive_mergeable(struct virtnet_info *vi, struct sk_buff *skb)
+{
+	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
+	struct page *page;
+	int num_buf, i, len;
+
+	num_buf = hdr->mhdr.num_buffers;
+	while (--num_buf) {
+		i = skb_shinfo(skb)->nr_frags;
+		if (i >= MAX_SKB_FRAGS) {
+			pr_debug("%s: packet too long\n", skb->dev->name);
+			skb->dev->stats.rx_length_errors++;
+			return -EINVAL;
+		}
 
-			skb_shinfo(skb)->frags[i].size = len;
-			skb_shinfo(skb)->nr_frags++;
-			skb->data_len += len;
-			skb->len += len;
+		page = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
+		if (!page) {
+			pr_debug("%s: rx error: %d buffers missing\n",
+				 skb->dev->name, hdr->mhdr.num_buffers);
+			skb->dev->stats.rx_length_errors++;
+			return -EINVAL;
 		}
-	} else {
-		len -= sizeof(hdr->hdr);
+		if (len > PAGE_SIZE)
+			len = PAGE_SIZE;
+
+		set_skb_frag(skb, page, 0, &len);
+
+		--vi->num;
+	}
+	return 0;
+}
+
+static void receive_buf(struct net_device *dev, void *buf, unsigned int len)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	struct sk_buff *skb;
+	struct page *page;
+	struct skb_vnet_hdr *hdr;
 
-		if (len <= MAX_PACKET_LEN)
-			trim_pages(vi, skb);
+	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
+		pr_debug("%s: short packet %i\n", dev->name, len);
+		dev->stats.rx_length_errors++;
+		if (vi->mergeable_rx_bufs || vi->big_packets)
+			give_pages(vi, buf);
+		else
+			dev_kfree_skb(buf);
+		return;
+	}
 
-		err = pskb_trim(skb, len);
-		if (err) {
-			pr_debug("%s: pskb_trim failed %i %d\n", dev->name,
-				 len, err);
+	if (!vi->mergeable_rx_bufs && !vi->big_packets) {
+		skb = buf;
+		len -= sizeof(struct virtio_net_hdr);
+		skb_trim(skb, len);
+	} else {
+		page = buf;
+		skb = page_to_skb(vi, page, len);
+		if (unlikely(!skb)) {
 			dev->stats.rx_dropped++;
-			goto drop;
+			give_pages(vi, page);
+			return;
 		}
+		if (vi->mergeable_rx_bufs)
+			if (receive_mergeable(vi, skb)) {
+				dev_kfree_skb(skb);
+				return;
+			}
 	}
 
+	hdr = skb_vnet_hdr(skb);
 	skb->truesize += skb->data_len;
 	dev->stats.rx_bytes += skb->len;
 	dev->stats.rx_packets++;
@@ -267,110 +319,119 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb,
 
 frame_err:
 	dev->stats.rx_frame_errors++;
-drop:
 	dev_kfree_skb(skb);
 }
 
-static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
+static int add_recvbuf_small(struct virtnet_info *vi, gfp_t gfp)
 {
 	struct sk_buff *skb;
-	struct scatterlist sg[2+MAX_SKB_FRAGS];
-	int num, err, i;
-	bool oom = false;
-
-	sg_init_table(sg, 2+MAX_SKB_FRAGS);
-	do {
-		struct skb_vnet_hdr *hdr;
+	struct skb_vnet_hdr *hdr;
+	struct scatterlist sg[2];
+	int err;
 
-		skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
-		if (unlikely(!skb)) {
-			oom = true;
-			break;
-		}
+	skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
+	if (unlikely(!skb))
+		return -ENOMEM;
 
-		skb_put(skb, MAX_PACKET_LEN);
+	skb_put(skb, MAX_PACKET_LEN);
 
-		hdr = skb_vnet_hdr(skb);
-		sg_set_buf(sg, &hdr->hdr, sizeof(hdr->hdr));
+	hdr = skb_vnet_hdr(skb);
+	sg_set_buf(sg, &hdr->hdr, sizeof hdr->hdr);
 
-		if (vi->big_packets) {
-			for (i = 0; i < MAX_SKB_FRAGS; i++) {
-				skb_frag_t *f = &skb_shinfo(skb)->frags[i];
-				f->page = get_a_page(vi, gfp);
-				if (!f->page)
-					break;
+	skb_to_sgvec(skb, sg + 1, 0, skb->len);
 
-				f->page_offset = 0;
-				f->size = PAGE_SIZE;
+	err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 2, skb);
+	if (err < 0)
+		dev_kfree_skb(skb);
 
-				skb->data_len += PAGE_SIZE;
-				skb->len += PAGE_SIZE;
+	return err;
+}
 
-				skb_shinfo(skb)->nr_frags++;
-			}
+static int add_recvbuf_big(struct virtnet_info *vi, gfp_t gfp)
+{
+	struct scatterlist sg[MAX_SKB_FRAGS + 2];
+	struct page *first, *list = NULL;
+	char *p;
+	int i, err, offset;
+
+	/* page in sg[MAX_SKB_FRAGS + 1] is list tail */
+	for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
+		first = get_a_page(vi, gfp);
+		if (!first) {
+			if (list)
+				give_pages(vi, list);
+			return -ENOMEM;
 		}
+		sg_set_buf(&sg[i], page_address(first), PAGE_SIZE);
 
-		num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
-		skb_queue_head(&vi->recv, skb);
+		/* chain new page in list head to match sg */
+		first->private = (unsigned long)list;
+		list = first;
+	}
 
-		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
-		if (err < 0) {
-			skb_unlink(skb, &vi->recv);
-			trim_pages(vi, skb);
-			kfree_skb(skb);
-			break;
-		}
-		vi->num++;
-	} while (err >= num);
-	if (unlikely(vi->num > vi->max))
-		vi->max = vi->num;
-	vi->rvq->vq_ops->kick(vi->rvq);
-	return !oom;
+	first = get_a_page(vi, gfp);
+	if (!first) {
+		give_pages(vi, list);
+		return -ENOMEM;
+	}
+	p = page_address(first);
+
+	/* sg[0], sg[1] share the same page */
+	/* a separated sg[0] for  virtio_net_hdr only during to QEMU bug*/
+	sg_set_buf(&sg[0], p, sizeof(struct virtio_net_hdr));
+
+	/* sg[1] for data packet, from offset */
+	offset = sizeof(struct padded_vnet_hdr);
+	sg_set_buf(&sg[1], p + offset, PAGE_SIZE - offset);
+
+	/* chain first in list head */
+	first->private = (unsigned long)list;
+	err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, MAX_SKB_FRAGS + 2,
+				       first);
+	if (err < 0)
+		give_pages(vi, first);
+
+	return err;
 }
 
-/* Returns false if we couldn't fill entirely (OOM). */
-static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
+static int add_recvbuf_mergeable(struct virtnet_info *vi, gfp_t gfp)
 {
-	struct sk_buff *skb;
-	struct scatterlist sg[1];
+	struct page *page;
+	struct scatterlist sg;
 	int err;
-	bool oom = false;
-
-	if (!vi->mergeable_rx_bufs)
-		return try_fill_recv_maxbufs(vi, gfp);
 
-	do {
-		skb_frag_t *f;
+	page = get_a_page(vi, gfp);
+	if (!page)
+		return -ENOMEM;
 
-		skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
-		if (unlikely(!skb)) {
-			oom = true;
-			break;
-		}
+	sg_init_one(&sg, page_address(page), PAGE_SIZE);
 
-		f = &skb_shinfo(skb)->frags[0];
-		f->page = get_a_page(vi, gfp);
-		if (!f->page) {
-			oom = true;
-			kfree_skb(skb);
-			break;
-		}
+	err = vi->rvq->vq_ops->add_buf(vi->rvq, &sg, 0, 1, page);
+	if (err < 0)
+		give_pages(vi, page);
 
-		f->page_offset = 0;
-		f->size = PAGE_SIZE;
+	return err;
+}
 
-		skb_shinfo(skb)->nr_frags++;
+/* Returns false if we couldn't fill entirely (OOM). */
+static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
+{
+	int err;
+	bool oom = false;
 
-		sg_init_one(sg, page_address(f->page), PAGE_SIZE);
-		skb_queue_head(&vi->recv, skb);
+	do {
+		if (vi->mergeable_rx_bufs)
+			err = add_recvbuf_mergeable(vi, gfp);
+		else if (vi->big_packets)
+			err = add_recvbuf_big(vi, gfp);
+		else
+			err = add_recvbuf_small(vi, gfp);
 
-		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
 		if (err < 0) {
-			skb_unlink(skb, &vi->recv);
-			kfree_skb(skb);
+			oom = true;
 			break;
 		}
-		vi->num++;
+		++vi->num;
 	} while (err > 0);
 	if (unlikely(vi->num > vi->max))
 		vi->max = vi->num;
@@ -408,15 +469,14 @@ static void refill_work(struct work_struct *work)
 static int virtnet_poll(struct napi_struct *napi, int budget)
 {
 	struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi);
-	struct sk_buff *skb = NULL;
+	void *buf;
 	unsigned int len, received = 0;
 
 again:
 	while (received < budget &&
-	       (skb = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) {
-		__skb_unlink(skb, &vi->recv);
-		receive_skb(vi->dev, skb, len);
-		vi->num--;
+	       (buf = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) {
+		receive_buf(vi->dev, buf, len);
+		--vi->num;
 		received++;
 	}
 
@@ -496,9 +556,9 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
 
 	/* Encode metadata header at front. */
 	if (vi->mergeable_rx_bufs)
-		sg_set_buf(sg, &hdr->mhdr, sizeof(hdr->mhdr));
+		sg_set_buf(sg, &hdr->mhdr, sizeof hdr->mhdr);
 	else
-		sg_set_buf(sg, &hdr->hdr, sizeof(hdr->hdr));
+		sg_set_buf(sg, &hdr->hdr, sizeof hdr->hdr);
 
 	hdr->num_sg = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
 	return vi->svq->vq_ops->add_buf(vi->svq, sg, hdr->num_sg, 0, skb);
@@ -916,8 +976,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 			dev->features |= NETIF_F_HW_VLAN_FILTER;
 	}
 
-	/* Initialize our empty receive and send queues. */
-	skb_queue_head_init(&vi->recv);
+	/* Initialize our empty send queue. */
 	skb_queue_head_init(&vi->send);
 
 	err = register_netdev(dev);
@@ -952,25 +1011,35 @@ free:
 	return err;
 }
 
+static void free_unused_bufs(struct virtnet_info *vi)
+{
+	void *buf;
+	while (1) {
+		buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
+		if (!buf)
+			break;
+		if (vi->mergeable_rx_bufs || vi->big_packets)
+			give_pages(vi, buf);
+		else
+			dev_kfree_skb(buf);
+		--vi->num;
+	}
+	BUG_ON(vi->num != 0);
+}
+
 static void __devexit virtnet_remove(struct virtio_device *vdev)
 {
 	struct virtnet_info *vi = vdev->priv;
-	struct sk_buff *skb;
 
 	/* Stop all the virtqueues. */
 	vdev->config->reset(vdev);
 
-	/* Free our skbs in send and recv queues, if any. */
-	while ((skb = __skb_dequeue(&vi->recv)) != NULL) {
-		kfree_skb(skb);
-		vi->num--;
-	}
+	/* Free our skbs in send queue, if any. */
 	__skb_queue_purge(&vi->send);
 
-	BUG_ON(vi->num != 0);
-
 	unregister_netdev(vi->dev);
 	cancel_delayed_work_sync(&vi->refill);
+	free_unused_bufs(vi);
 
 	vdev->config->del_vqs(vi->vdev);
 

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Michael S. Tsirkin]

On Wed, Jan 13, 2010 at 12:53:38PM -0800, Shirley Ma wrote:
> virtio_net receives packets from its pre-allocated vring buffers, then it 
> delivers these packets to upper layer protocols as skb buffs. So it's not
> necessary to pre-allocate skb for each mergable buffer, then frees extra 
> skbs when buffers are merged into a large packet. This patch has deferred 
> skb allocation in receiving packets for both big packets and mergeable buffers
> to reduce skb pre-allocations and skb frees. It frees unused buffers by calling 
> detach_unused_buf in vring, so recv skb queue is not needed.
> 
> Signed-off-by: Shirley Ma <xma@us.ibm.com>
> ---
>  drivers/net/virtio_net.c |  427 +++++++++++++++++++++++++++-------------------
>  1 files changed, 248 insertions(+), 179 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c708ecc..72b3f21 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -56,8 +56,7 @@ struct virtnet_info
>  	/* Host will merge rx buffers for big packets (shake it! shake it!) */
>  	bool mergeable_rx_bufs;
>  
> -	/* Receive & send queues. */
> -	struct sk_buff_head recv;
> +	/* Send queue. */
>  	struct sk_buff_head send;
>

How hard is it to get rid of send queue, btw?
  
>  	/* Work struct for refilling if we run low on memory. */
> @@ -75,34 +74,44 @@ struct skb_vnet_hdr {
>  	unsigned int num_sg;
>  };
>  
> +struct padded_vnet_hdr {
> +	struct virtio_net_hdr hdr;
> +	/*
> +	 * virtio_net_hdr should be in a separated sg buffer because of a
> +	 * QEMU bug, and data sg buffer shares same page with this header sg.
> +	 * This padding makes next sg 16 byte aligned after virtio_net_hdr.
> +	 */
> +	char padding[6];
> +};
> +
>  static inline struct skb_vnet_hdr *skb_vnet_hdr(struct sk_buff *skb)
>  {
>  	return (struct skb_vnet_hdr *)skb->cb;
>  }
>  
> -static void give_a_page(struct virtnet_info *vi, struct page *page)
> -{
> -	page->private = (unsigned long)vi->pages;
> -	vi->pages = page;
> -}
> -
> -static void trim_pages(struct virtnet_info *vi, struct sk_buff *skb)
> +/*
> + * private is used to chain pages for big packets, put the whole
> + * most recent used list in the beginning for reuse
> + */
> +static void give_pages(struct virtnet_info *vi, struct page *page)
>  {
> -	unsigned int i;
> +	struct page *end;
>  
> -	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
> -		give_a_page(vi, skb_shinfo(skb)->frags[i].page);
> -	skb_shinfo(skb)->nr_frags = 0;
> -	skb->data_len = 0;
> +	/* Find end of list, sew whole thing into vi->pages. */
> +	for (end = page; end->private; end = (struct page *)end->private);
> +	end->private = (unsigned long)vi->pages;
> +	vi->pages = page;
>  }
>  
>  static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
>  {
>  	struct page *p = vi->pages;
>  
> -	if (p)
> +	if (p) {
>  		vi->pages = (struct page *)p->private;
> -	else
> +		/* clear private here, it is used to chain pages */
> +		p->private = 0;
> +	} else
>  		p = alloc_page(gfp_mask);
>  	return p;
>  }
> @@ -118,99 +127,142 @@ static void skb_xmit_done(struct virtqueue *svq)
>  	netif_wake_queue(vi->dev);
>  }
>  
> -static void receive_skb(struct net_device *dev, struct sk_buff *skb,
> -			unsigned len)
> +static void set_skb_frag(struct sk_buff *skb, struct page *page,
> +			 unsigned int offset, unsigned int *len)
>  {
> -	struct virtnet_info *vi = netdev_priv(dev);
> -	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
> -	int err;
> -	int i;
> -
> -	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
> -		pr_debug("%s: short packet %i\n", dev->name, len);
> -		dev->stats.rx_length_errors++;
> -		goto drop;
> -	}
> +	int i = skb_shinfo(skb)->nr_frags;
> +	skb_frag_t *f;
> +
> +	f = &skb_shinfo(skb)->frags[i];
> +	f->size = min((unsigned)PAGE_SIZE - offset, *len);
> +	f->page_offset = offset;
> +	f->page = page;
> +
> +	skb->data_len += f->size;
> +	skb->len += f->size;
> +	skb_shinfo(skb)->nr_frags++;
> +	*len -= f->size;
> +}
>  
> -	if (vi->mergeable_rx_bufs) {
> -		unsigned int copy;
> -		char *p = page_address(skb_shinfo(skb)->frags[0].page);
> +static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> +				   struct page *page, unsigned int len)
> +{
> +	struct sk_buff *skb;
> +	struct skb_vnet_hdr *hdr;
> +	unsigned int copy, hdr_len, offset;
> +	char *p;
>  
> -		if (len > PAGE_SIZE)
> -			len = PAGE_SIZE;
> -		len -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
> +	p = page_address(page);
>  
> -		memcpy(&hdr->mhdr, p, sizeof(hdr->mhdr));
> -		p += sizeof(hdr->mhdr);
> +	/* copy small packet so we can reuse these pages for small data */
> +	skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
> +	if (unlikely(!skb))
> +		return NULL;
>  
> -		copy = len;
> -		if (copy > skb_tailroom(skb))
> -			copy = skb_tailroom(skb);
> +	hdr = skb_vnet_hdr(skb);
>  
> -		memcpy(skb_put(skb, copy), p, copy);
> +	if (vi->mergeable_rx_bufs) {
> +		hdr_len = sizeof hdr->mhdr;
> +		offset = hdr_len;
> +	} else {
> +		hdr_len = sizeof hdr->hdr;
> +		offset = sizeof(struct padded_vnet_hdr);
> +	}
>  
> -		len -= copy;
> +	memcpy(hdr, p, hdr_len);
>  
> -		if (!len) {
> -			give_a_page(vi, skb_shinfo(skb)->frags[0].page);
> -			skb_shinfo(skb)->nr_frags--;
> -		} else {
> -			skb_shinfo(skb)->frags[0].page_offset +=
> -				sizeof(hdr->mhdr) + copy;
> -			skb_shinfo(skb)->frags[0].size = len;
> -			skb->data_len += len;
> -			skb->len += len;
> -		}
> +	len -= hdr_len;
> +	p += offset;
>  
> -		while (--hdr->mhdr.num_buffers) {
> -			struct sk_buff *nskb;
> +	copy = len;
> +	if (copy > skb_tailroom(skb))
> +		copy = skb_tailroom(skb);
> +	memcpy(skb_put(skb, copy), p, copy);
>  
> -			i = skb_shinfo(skb)->nr_frags;
> -			if (i >= MAX_SKB_FRAGS) {
> -				pr_debug("%s: packet too long %d\n", dev->name,
> -					 len);
> -				dev->stats.rx_length_errors++;
> -				goto drop;
> -			}
> +	len -= copy;
> +	offset += copy;
>  
> -			nskb = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
> -			if (!nskb) {
> -				pr_debug("%s: rx error: %d buffers missing\n",
> -					 dev->name, hdr->mhdr.num_buffers);
> -				dev->stats.rx_length_errors++;
> -				goto drop;
> -			}
> +	while (len) {
> +		set_skb_frag(skb, page, offset, &len);
> +		page = (struct page *)page->private;
> +		offset = 0;
> +	}
>  
> -			__skb_unlink(nskb, &vi->recv);
> -			vi->num--;
> +	if (page)
> +		give_pages(vi, page);
>  
> -			skb_shinfo(skb)->frags[i] = skb_shinfo(nskb)->frags[0];
> -			skb_shinfo(nskb)->nr_frags = 0;
> -			kfree_skb(nskb);
> +	return skb;
> +}
>  
> -			if (len > PAGE_SIZE)
> -				len = PAGE_SIZE;
> +static int receive_mergeable(struct virtnet_info *vi, struct sk_buff *skb)
> +{
> +	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
> +	struct page *page;
> +	int num_buf, i, len;
> +
> +	num_buf = hdr->mhdr.num_buffers;
> +	while (--num_buf) {
> +		i = skb_shinfo(skb)->nr_frags;
> +		if (i >= MAX_SKB_FRAGS) {
> +			pr_debug("%s: packet too long\n", skb->dev->name);
> +			skb->dev->stats.rx_length_errors++;
> +			return -EINVAL;
> +		}
>  
> -			skb_shinfo(skb)->frags[i].size = len;
> -			skb_shinfo(skb)->nr_frags++;
> -			skb->data_len += len;
> -			skb->len += len;
> +		page = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
> +		if (!page) {
> +			pr_debug("%s: rx error: %d buffers missing\n",
> +				 skb->dev->name, hdr->mhdr.num_buffers);
> +			skb->dev->stats.rx_length_errors++;
> +			return -EINVAL;
>  		}
> -	} else {
> -		len -= sizeof(hdr->hdr);
> +		if (len > PAGE_SIZE)
> +			len = PAGE_SIZE;
> +
> +		set_skb_frag(skb, page, 0, &len);
> +
> +		--vi->num;
> +	}
> +	return 0;
> +}
> +
> +static void receive_buf(struct net_device *dev, void *buf, unsigned int len)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	struct sk_buff *skb;
> +	struct page *page;
> +	struct skb_vnet_hdr *hdr;
>  
> -		if (len <= MAX_PACKET_LEN)
> -			trim_pages(vi, skb);
> +	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
> +		pr_debug("%s: short packet %i\n", dev->name, len);
> +		dev->stats.rx_length_errors++;
> +		if (vi->mergeable_rx_bufs || vi->big_packets)
> +			give_pages(vi, buf);
> +		else
> +			dev_kfree_skb(buf);
> +		return;
> +	}
>  
> -		err = pskb_trim(skb, len);
> -		if (err) {
> -			pr_debug("%s: pskb_trim failed %i %d\n", dev->name,
> -				 len, err);
> +	if (!vi->mergeable_rx_bufs && !vi->big_packets) {
> +		skb = buf;
> +		len -= sizeof(struct virtio_net_hdr);
> +		skb_trim(skb, len);
> +	} else {
> +		page = buf;
> +		skb = page_to_skb(vi, page, len);
> +		if (unlikely(!skb)) {
>  			dev->stats.rx_dropped++;
> -			goto drop;
> +			give_pages(vi, page);
> +			return;
>  		}
> +		if (vi->mergeable_rx_bufs)
> +			if (receive_mergeable(vi, skb)) {
> +				dev_kfree_skb(skb);
> +				return;
> +			}
>  	}
>  
> +	hdr = skb_vnet_hdr(skb);
>  	skb->truesize += skb->data_len;
>  	dev->stats.rx_bytes += skb->len;
>  	dev->stats.rx_packets++;
> @@ -267,110 +319,119 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb,
>  
>  frame_err:
>  	dev->stats.rx_frame_errors++;
> -drop:
>  	dev_kfree_skb(skb);
>  }
>  
> -static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
> +static int add_recvbuf_small(struct virtnet_info *vi, gfp_t gfp)
>  {
>  	struct sk_buff *skb;
> -	struct scatterlist sg[2+MAX_SKB_FRAGS];
> -	int num, err, i;
> -	bool oom = false;
> -
> -	sg_init_table(sg, 2+MAX_SKB_FRAGS);
> -	do {
> -		struct skb_vnet_hdr *hdr;
> +	struct skb_vnet_hdr *hdr;
> +	struct scatterlist sg[2];
> +	int err;
>  
> -		skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
> -		if (unlikely(!skb)) {
> -			oom = true;
> -			break;
> -		}
> +	skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
> +	if (unlikely(!skb))
> +		return -ENOMEM;
>  
> -		skb_put(skb, MAX_PACKET_LEN);
> +	skb_put(skb, MAX_PACKET_LEN);
>  
> -		hdr = skb_vnet_hdr(skb);
> -		sg_set_buf(sg, &hdr->hdr, sizeof(hdr->hdr));
> +	hdr = skb_vnet_hdr(skb);
> +	sg_set_buf(sg, &hdr->hdr, sizeof hdr->hdr);
>  
> -		if (vi->big_packets) {
> -			for (i = 0; i < MAX_SKB_FRAGS; i++) {
> -				skb_frag_t *f = &skb_shinfo(skb)->frags[i];
> -				f->page = get_a_page(vi, gfp);
> -				if (!f->page)
> -					break;
> +	skb_to_sgvec(skb, sg + 1, 0, skb->len);
>  
> -				f->page_offset = 0;
> -				f->size = PAGE_SIZE;
> +	err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 2, skb);
> +	if (err < 0)
> +		dev_kfree_skb(skb);
>  
> -				skb->data_len += PAGE_SIZE;
> -				skb->len += PAGE_SIZE;
> +	return err;
> +}
>  
> -				skb_shinfo(skb)->nr_frags++;
> -			}
> +static int add_recvbuf_big(struct virtnet_info *vi, gfp_t gfp)
> +{
> +	struct scatterlist sg[MAX_SKB_FRAGS + 2];
> +	struct page *first, *list = NULL;
> +	char *p;
> +	int i, err, offset;
> +
> +	/* page in sg[MAX_SKB_FRAGS + 1] is list tail */
> +	for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
> +		first = get_a_page(vi, gfp);
> +		if (!first) {
> +			if (list)
> +				give_pages(vi, list);
> +			return -ENOMEM;
>  		}
> +		sg_set_buf(&sg[i], page_address(first), PAGE_SIZE);
>  
> -		num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
> -		skb_queue_head(&vi->recv, skb);
> +		/* chain new page in list head to match sg */
> +		first->private = (unsigned long)list;
> +		list = first;
> +	}
>  
> -		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
> -		if (err < 0) {
> -			skb_unlink(skb, &vi->recv);
> -			trim_pages(vi, skb);
> -			kfree_skb(skb);
> -			break;
> -		}
> -		vi->num++;
> -	} while (err >= num);
> -	if (unlikely(vi->num > vi->max))
> -		vi->max = vi->num;
> -	vi->rvq->vq_ops->kick(vi->rvq);
> -	return !oom;
> +	first = get_a_page(vi, gfp);
> +	if (!first) {
> +		give_pages(vi, list);
> +		return -ENOMEM;
> +	}
> +	p = page_address(first);
> +
> +	/* sg[0], sg[1] share the same page */
> +	/* a separated sg[0] for  virtio_net_hdr only during to QEMU bug*/
> +	sg_set_buf(&sg[0], p, sizeof(struct virtio_net_hdr));
> +
> +	/* sg[1] for data packet, from offset */
> +	offset = sizeof(struct padded_vnet_hdr);
> +	sg_set_buf(&sg[1], p + offset, PAGE_SIZE - offset);
> +
> +	/* chain first in list head */
> +	first->private = (unsigned long)list;
> +	err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, MAX_SKB_FRAGS + 2,
> +				       first);
> +	if (err < 0)
> +		give_pages(vi, first);
> +
> +	return err;
>  }
>  
> -/* Returns false if we couldn't fill entirely (OOM). */
> -static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
> +static int add_recvbuf_mergeable(struct virtnet_info *vi, gfp_t gfp)
>  {
> -	struct sk_buff *skb;
> -	struct scatterlist sg[1];
> +	struct page *page;
> +	struct scatterlist sg;
>  	int err;
> -	bool oom = false;
> -
> -	if (!vi->mergeable_rx_bufs)
> -		return try_fill_recv_maxbufs(vi, gfp);
>  
> -	do {
> -		skb_frag_t *f;
> +	page = get_a_page(vi, gfp);
> +	if (!page)
> +		return -ENOMEM;
>  
> -		skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
> -		if (unlikely(!skb)) {
> -			oom = true;
> -			break;
> -		}
> +	sg_init_one(&sg, page_address(page), PAGE_SIZE);
>  
> -		f = &skb_shinfo(skb)->frags[0];
> -		f->page = get_a_page(vi, gfp);
> -		if (!f->page) {
> -			oom = true;
> -			kfree_skb(skb);
> -			break;
> -		}
> +	err = vi->rvq->vq_ops->add_buf(vi->rvq, &sg, 0, 1, page);
> +	if (err < 0)
> +		give_pages(vi, page);
>  
> -		f->page_offset = 0;
> -		f->size = PAGE_SIZE;
> +	return err;
> +}
>  
> -		skb_shinfo(skb)->nr_frags++;
> +/* Returns false if we couldn't fill entirely (OOM). */
> +static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
> +{
> +	int err;
> +	bool oom = false;
>  
> -		sg_init_one(sg, page_address(f->page), PAGE_SIZE);
> -		skb_queue_head(&vi->recv, skb);
> +	do {
> +		if (vi->mergeable_rx_bufs)
> +			err = add_recvbuf_mergeable(vi, gfp);
> +		else if (vi->big_packets)
> +			err = add_recvbuf_big(vi, gfp);
> +		else
> +			err = add_recvbuf_small(vi, gfp);
>  
> -		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
>  		if (err < 0) {
> -			skb_unlink(skb, &vi->recv);
> -			kfree_skb(skb);
> +			oom = true;
>  			break;
>  		}
> -		vi->num++;
> +		++vi->num;
>  	} while (err > 0);
>  	if (unlikely(vi->num > vi->max))
>  		vi->max = vi->num;
> @@ -408,15 +469,14 @@ static void refill_work(struct work_struct *work)
>  static int virtnet_poll(struct napi_struct *napi, int budget)
>  {
>  	struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi);
> -	struct sk_buff *skb = NULL;
> +	void *buf;
>  	unsigned int len, received = 0;
>  
>  again:
>  	while (received < budget &&
> -	       (skb = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) {
> -		__skb_unlink(skb, &vi->recv);
> -		receive_skb(vi->dev, skb, len);
> -		vi->num--;
> +	       (buf = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) {
> +		receive_buf(vi->dev, buf, len);
> +		--vi->num;
>  		received++;
>  	}
>  
> @@ -496,9 +556,9 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
>  
>  	/* Encode metadata header at front. */
>  	if (vi->mergeable_rx_bufs)
> -		sg_set_buf(sg, &hdr->mhdr, sizeof(hdr->mhdr));
> +		sg_set_buf(sg, &hdr->mhdr, sizeof hdr->mhdr);
>  	else
> -		sg_set_buf(sg, &hdr->hdr, sizeof(hdr->hdr));
> +		sg_set_buf(sg, &hdr->hdr, sizeof hdr->hdr);
>  
>  	hdr->num_sg = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
>  	return vi->svq->vq_ops->add_buf(vi->svq, sg, hdr->num_sg, 0, skb);
> @@ -916,8 +976,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  			dev->features |= NETIF_F_HW_VLAN_FILTER;
>  	}
>  
> -	/* Initialize our empty receive and send queues. */
> -	skb_queue_head_init(&vi->recv);
> +	/* Initialize our empty send queue. */
>  	skb_queue_head_init(&vi->send);
>  
>  	err = register_netdev(dev);
> @@ -952,25 +1011,35 @@ free:
>  	return err;
>  }
>  
> +static void free_unused_bufs(struct virtnet_info *vi)
> +{
> +	void *buf;
> +	while (1) {
> +		buf = vi->rvq->vq_ops->detach_unused_buf(vi->rvq);
> +		if (!buf)
> +			break;
> +		if (vi->mergeable_rx_bufs || vi->big_packets)
> +			give_pages(vi, buf);
> +		else
> +			dev_kfree_skb(buf);
> +		--vi->num;
> +	}
> +	BUG_ON(vi->num != 0);
> +}
> +
>  static void __devexit virtnet_remove(struct virtio_device *vdev)
>  {
>  	struct virtnet_info *vi = vdev->priv;
> -	struct sk_buff *skb;
>  
>  	/* Stop all the virtqueues. */
>  	vdev->config->reset(vdev);
>  
> -	/* Free our skbs in send and recv queues, if any. */
> -	while ((skb = __skb_dequeue(&vi->recv)) != NULL) {
> -		kfree_skb(skb);
> -		vi->num--;
> -	}
> +	/* Free our skbs in send queue, if any. */
>  	__skb_queue_purge(&vi->send);
>  
> -	BUG_ON(vi->num != 0);
> -
>  	unregister_netdev(vi->dev);
>  	cancel_delayed_work_sync(&vi->refill);
> +	free_unused_bufs(vi);
>  
>  	vdev->config->del_vqs(vi->vdev);
>  
> 

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

On Wed, 2010-01-13 at 22:57 +0200, Michael S. Tsirkin wrote:
> How hard is it to get rid of send queue, btw?

Pretty straight forward. I prefer a separate patch for send side so I
didn't include it in this patch.

Thanks
Shirley

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Michael S. Tsirkin]

On Wed, Jan 13, 2010 at 01:33:41PM -0800, Shirley Ma wrote:
> On Wed, 2010-01-13 at 22:57 +0200, Michael S. Tsirkin wrote:
> > How hard is it to get rid of send queue, btw?
> 
> Pretty straight forward. I prefer a separate patch for send side so I
> didn't include it in this patch.
> 
> Thanks
> Shirley

Yes, separate patch is best.

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

On Wed, 2010-01-13 at 23:37 +0200, Michael S. Tsirkin wrote:
> Yes, separate patch is best.

The send side patch is done, I will submit it when this patch has been
reviewed. :)

thanks
Shirley

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Michael S. Tsirkin]

On Wed, Jan 13, 2010 at 02:23:48PM -0800, Shirley Ma wrote:
> On Wed, 2010-01-13 at 23:37 +0200, Michael S. Tsirkin wrote:
> > Yes, separate patch is best.
> 
> The send side patch is done, I will submit it when this patch has been
> reviewed. :)


Hey, why wait :)

> thanks
> Shirley

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

On Thu, 2010-01-14 at 00:48 +0200, Michael S. Tsirkin wrote:
> On Wed, Jan 13, 2010 at 02:23:48PM -0800, Shirley Ma wrote:
> > On Wed, 2010-01-13 at 23:37 +0200, Michael S. Tsirkin wrote:
> > > Yes, separate patch is best.
> > 
> > The send side patch is done, I will submit it when this patch has
> been
> > reviewed. :)
> 
> 
> Hey, why wait :)
> 

Because: the send side patch is built on top of this patch and uses
free_unused_bufs() func.

Thanks
Shirley

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Rusty Russell]

On Thu, 14 Jan 2010 07:23:38 am Shirley Ma wrote:
> virtio_net receives packets from its pre-allocated vring buffers, then it 
> delivers these packets to upper layer protocols as skb buffs. So it's not
> necessary to pre-allocate skb for each mergable buffer, then frees extra 
> skbs when buffers are merged into a large packet. This patch has deferred 
> skb allocation in receiving packets for both big packets and mergeable buffers
> to reduce skb pre-allocations and skb frees. It frees unused buffers by calling 
> detach_unused_buf in vring, so recv skb queue is not needed.
> 
> Signed-off-by: Shirley Ma <xma@us.ibm.com>

Thanks, applied!

After testing I'll send it to DaveM.

Rusty.

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Michael S. Tsirkin]

On Wed, Jan 13, 2010 at 04:37:55PM -0800, Shirley Ma wrote:
> On Thu, 2010-01-14 at 00:48 +0200, Michael S. Tsirkin wrote:
> > On Wed, Jan 13, 2010 at 02:23:48PM -0800, Shirley Ma wrote:
> > > On Wed, 2010-01-13 at 23:37 +0200, Michael S. Tsirkin wrote:
> > > > Yes, separate patch is best.
> > > 
> > > The send side patch is done, I will submit it when this patch has
> > > been reviewed. :)
> > 
> > 
> > Hey, why wait :)
> > 
> 
> Because: the send side patch is built on top of this patch and uses
> free_unused_bufs() func.
> 
> Thanks
> Shirley

Now that's in, how does the send patch look?

-- 
MST

Re: [PATCH v2 2/2] virtio_net: Defer skb allocation in receive path

[Shirley Ma]

On Fri, 2010-01-29 at 16:05 +0200, Michael S. Tsirkin wrote:
> 
> Now that's in, how does the send patch look? 

Thanks. I will submit it today. It's a simple patch.

Shirley