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Commit fb6813f4 authored by Rusty Russell's avatar Rusty Russell
Browse files

virtio: Recycle unused recv buffer pages for large skbs in net driver 



If we hack the virtio_net driver to always allocate full-sized (64k+)
skbuffs, the driver slows down (lguest numbers):

  Time to receive 1GB (small buffers): 10.85 seconds
  Time to receive 1GB (64k+ buffers): 24.75 seconds

Of course, large buffers use up more space in the ring, so we increase
that from 128 to 2048:

  Time to receive 1GB (64k+ buffers, 2k ring): 16.61 seconds

If we recycle pages rather than using alloc_page/free_page:

  Time to receive 1GB (64k+ buffers, 2k ring, recycle pages): 10.81 seconds

This demonstrates that with efficient allocation, we don't need to
have a separate "small buffer" queue.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 97402b96

drivers/net/virtio_net.c

+35 −1
Original line number Diff line number Diff line
@@ -61,6 +61,9 @@ struct virtnet_info 
	/* Receive & send queues. */

	struct sk_buff_head recv;

	struct sk_buff_head send;



	/* Chain pages by the private ptr. */

	struct page *pages;

};



static inline struct virtio_net_hdr *skb_vnet_hdr(struct sk_buff *skb)
@@ -73,6 +76,23 @@ static inline void vnet_hdr_to_sg(struct scatterlist *sg, struct sk_buff *skb) 
	sg_init_one(sg, skb_vnet_hdr(skb), sizeof(struct virtio_net_hdr));

}



static void give_a_page(struct virtnet_info *vi, struct page *page)

{

	page->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)

		vi->pages = (struct page *)p->private;

	else

		p = alloc_page(gfp_mask);

	return p;

}



static void skb_xmit_done(struct virtqueue *svq)

{

	struct virtnet_info *vi = svq->vdev->priv;
@@ -101,6 +121,15 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb, 
	}

	len -= sizeof(struct virtio_net_hdr);



	if (len <= MAX_PACKET_LEN) {

		unsigned int i;



		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)

			give_a_page(dev->priv, skb_shinfo(skb)->frags[i].page);

		skb->data_len = 0;

		skb_shinfo(skb)->nr_frags = 0;

	}



	err = pskb_trim(skb, len);

	if (err) {

		pr_debug("%s: pskb_trim failed %i %d\n", dev->name, len, err);
@@ -183,7 +212,7 @@ static void try_fill_recv(struct virtnet_info *vi) 
		if (vi->big_packets) {

			for (i = 0; i < MAX_SKB_FRAGS; i++) {

				skb_frag_t *f = &skb_shinfo(skb)->frags[i];

				f->page = alloc_page(GFP_ATOMIC);

				f->page = get_a_page(vi, GFP_ATOMIC);

				if (!f->page)

					break;
@@ -506,6 +535,7 @@ static int virtnet_probe(struct virtio_device *vdev) 
	vi->dev = dev;

	vi->vdev = vdev;

	vdev->priv = vi;

	vi->pages = NULL;



	/* If they give us a callback when all buffers are done, we don't need

	 * the timer. */
@@ -591,6 +621,10 @@ static void virtnet_remove(struct virtio_device *vdev) 
	vdev->config->del_vq(vi->svq);

	vdev->config->del_vq(vi->rvq);

	unregister_netdev(vi->dev);



	while (vi->pages)

		__free_pages(get_a_page(vi, GFP_KERNEL), 0);



	free_netdev(vi->dev);

}