[PATCH v2 4/4] Defer skb allocation -- change allocation &receiving in recv path

[Shirley Ma]

Signed-off-by: Shirley Ma <xma@xxxxxxxxxx>
-------------

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index dde8060..b919169 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -270,99 +270,44 @@ static struct sk_buff *receive_mergeable(struct virtnet_info *vi,
 	return skb;
 }
 
-static void receive_skb(struct net_device *dev, struct sk_buff *skb,
-			unsigned len)
+static void receive_buf(struct net_device *dev, void *buf, unsigned int len)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
-	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
-	int err;
-	int i;
+	struct sk_buff *skb = (struct sk_buff *)buf;
+	struct page *page = (struct page *)buf;
+	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++;
-		goto drop;
-	}
-
-	if (vi->mergeable_rx_bufs) {
-		unsigned int copy;
-		char *p = page_address(skb_shinfo(skb)->frags[0].page);
-
-		if (len > PAGE_SIZE)
-			len = PAGE_SIZE;
-		len -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
-
-		memcpy(&hdr->mhdr, p, sizeof(hdr->mhdr));
-		p += sizeof(hdr->mhdr);
-
-		copy = len;
-		if (copy > skb_tailroom(skb))
-			copy = skb_tailroom(skb);
-
-		memcpy(skb_put(skb, copy), p, copy);
-
-		len -= copy;
-
-		if (!len) {
-			give_pages(vi, skb_shinfo(skb)->frags[0].page);
-			skb_shinfo(skb)->nr_frags--;
+		if (vi->mergeable_rx_bufs || vi->big_packets) {
+			give_pages(vi, page);
+			return;
 		} 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;
-		}
-
-		while (--hdr->mhdr.num_buffers) {
-			struct sk_buff *nskb;
-
-			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;
-			}
-
-			__skb_unlink(nskb, &vi->recv);
-			vi->num--;
-
-			skb_shinfo(skb)->frags[i] = skb_shinfo(nskb)->frags[0];
-			skb_shinfo(nskb)->nr_frags = 0;
-			kfree_skb(nskb);
-
-			if (len > PAGE_SIZE)
-				len = PAGE_SIZE;
-
-			skb_shinfo(skb)->frags[i].size = len;
-			skb_shinfo(skb)->nr_frags++;
-			skb->data_len += len;
-			skb->len += len;
+			skb_unlink(skb, &vi->recv);
+			goto drop;
 		}
-	} else {
-		len -= sizeof(hdr->hdr);
+	}
 
-		if (len <= MAX_PACKET_LEN)
-			trim_pages(vi, skb);
+	if (vi->mergeable_rx_bufs)
+		skb = receive_mergeable(vi, page, len);
+	else if (vi->big_packets)
+		skb = receive_big(vi, page, len);
+	else {
+		__skb_unlink(skb, &vi->recv);
+		len -= sizeof(struct virtio_net_hdr);
+		skb_trim(skb, len);
+	}
 
-		err = pskb_trim(skb, len);
-		if (err) {
-			pr_debug("%s: pskb_trim failed %i %d\n", dev->name,
-				 len, err);
-			dev->stats.rx_dropped++;
-			goto drop;
-		}
+	if (unlikely(!skb)) {
+		dev->stats.rx_dropped++;
+		/* only for mergeable buf and big packets */
+		give_pages(vi, page);
+		return;
 	}
 
+	hdr = skb_vnet_hdr(skb);
+
 	skb->truesize += skb->data_len;
 	dev->stats.rx_bytes += skb->len;
 	dev->stats.rx_packets++;
@@ -520,105 +465,22 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi, gfp_t gfp, bool *oom)
 	return err;
 }
 
-static bool try_fill_recv_maxbufs(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;
-
-		skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
-		if (unlikely(!skb)) {
-			oom = true;
-			break;
-		}
-
-		skb_put(skb, MAX_PACKET_LEN);
-
-		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;
-
-				f->page_offset = 0;
-				f->size = PAGE_SIZE;
-
-				skb->data_len += PAGE_SIZE;
-				skb->len += PAGE_SIZE;
-
-				skb_shinfo(skb)->nr_frags++;
-			}
-		}
-
-		num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
-		skb_queue_head(&vi->recv, skb);
-
-		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;
-}
-
 /* Returns false if we couldn't fill entirely (OOM). */
 static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
 {
-	struct sk_buff *skb;
-	struct scatterlist sg[1];
 	int err;
 	bool oom = false;
 
-	if (!vi->mergeable_rx_bufs)
-		return try_fill_recv_maxbufs(vi, gfp);
-
 	do {
-		skb_frag_t *f;
-
-		skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
-		if (unlikely(!skb)) {
-			oom = true;
-			break;
-		}
-
-		f = &skb_shinfo(skb)->frags[0];
-		f->page = get_a_page(vi, gfp);
-		if (!f->page) {
-			oom = true;
-			kfree_skb(skb);
-			break;
-		}
-
-		f->page_offset = 0;
-		f->size = PAGE_SIZE;
-
-		skb_shinfo(skb)->nr_frags++;
-
-		sg_init_one(sg, page_address(f->page), PAGE_SIZE);
-		skb_queue_head(&vi->recv, skb);
+		if (vi->mergeable_rx_bufs)
+			err = add_recvbuf_mergeable(vi, gfp, &oom);
+		else if (vi->big_packets)
+			err = add_recvbuf_big(vi, gfp, &oom);
+		else
+			err = add_recvbuf_small(vi, gfp, &oom);
 
-		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
-		if (err < 0) {
-			skb_unlink(skb, &vi->recv);
-			kfree_skb(skb);
+		if (oom || err < 0)
 			break;
-		}
 		vi->num++;
 	} while (err > 0);
 	if (unlikely(vi->num > vi->max))
@@ -657,14 +519,13 @@ 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 = NULL;
 	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);
+	       (buf = vi->rvq->vq_ops->get_buf(vi->rvq, &len)) != NULL) {
+		receive_buf(vi->dev, buf, len);
 		vi->num--;
 		received++;
 	}
@@ -1205,6 +1066,7 @@ static void __devexit virtnet_remove(struct virtio_device *vdev)
 {
 	struct virtnet_info *vi = vdev->priv;
 	struct sk_buff *skb;
+	int freed;
 
 	/* Stop all the virtqueues. */
 	vdev->config->reset(vdev);
@@ -1216,11 +1078,14 @@ static void __devexit virtnet_remove(struct virtio_device *vdev)
 	}
 	__skb_queue_purge(&vi->send);
 
-	BUG_ON(vi->num != 0);
-
 	unregister_netdev(vi->dev);
 	cancel_delayed_work_sync(&vi->refill);
 
+	freed = vi->rvq->vq_ops->destroy_bufs(vi->rvq, virtio_net_free_pages);
+	vi->num -= freed;
+
+	BUG_ON(vi->num != 0);
+
 	vdev->config->del_vqs(vi->vdev);
 
 	while (vi->pages)


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