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

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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: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2008-07-25 12:06:01 -05:00
parent 97402b96f8
commit fb6813f480
1 changed files with 35 additions and 1 deletions
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36
drivers/net/virtio_net.c
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@ -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);
}