virtio_net: Defer skb allocation in receive path Date: Wed, 13 Jan 2010 12:53:38 -0800

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>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Shirley Ma 2010-01-29 03:20:04 +00:00 committed by David S. Miller
parent f9bfbebf34
commit 9ab86bbcf8
1 changed files with 257 additions and 188 deletions

View File

@ -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)
/*
* 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)
{
page->private = (unsigned long)vi->pages;
struct page *end;
/* 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 void trim_pages(struct virtnet_info *vi, struct sk_buff *skb)
{
unsigned int i;
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;
}
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)
{
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;
}
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;
p = page_address(page);
/* 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;
hdr = skb_vnet_hdr(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(hdr, p, hdr_len);
len -= hdr_len;
p += offset;
copy = len;
if (copy > skb_tailroom(skb))
copy = skb_tailroom(skb);
memcpy(skb_put(skb, copy), p, copy);
len -= copy;
offset += copy;
while (len) {
set_skb_frag(skb, page, offset, &len);
page = (struct page *)page->private;
offset = 0;
}
if (page)
give_pages(vi, page);
return skb;
}
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;
}
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;
}
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 skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
int err;
int i;
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++;
goto drop;
if (vi->mergeable_rx_bufs || vi->big_packets)
give_pages(vi, buf);
else
dev_kfree_skb(buf);
return;
}
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_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;
}
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;
}
if (!vi->mergeable_rx_bufs && !vi->big_packets) {
skb = buf;
len -= sizeof(struct virtio_net_hdr);
skb_trim(skb, len);
} else {
len -= sizeof(hdr->hdr);
if (len <= MAX_PACKET_LEN)
trim_pages(vi, skb);
err = pskb_trim(skb, len);
if (err) {
pr_debug("%s: pskb_trim failed %i %d\n", dev->name,
len, err);
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;
struct skb_vnet_hdr *hdr;
struct scatterlist sg[2];
int err;
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))
return -ENOMEM;
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);
skb_to_sgvec(skb, sg + 1, 0, skb->len);
err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 2, skb);
if (err < 0)
dev_kfree_skb(skb);
return err;
}
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);
skb_put(skb, MAX_PACKET_LEN);
/* chain new page in list head to match sg */
first->private = (unsigned long)list;
list = first;
}
hdr = skb_vnet_hdr(skb);
sg_set_buf(sg, &hdr->hdr, sizeof(hdr->hdr));
first = get_a_page(vi, gfp);
if (!first) {
give_pages(vi, list);
return -ENOMEM;
}
p = page_address(first);
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;
/* 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));
f->page_offset = 0;
f->size = PAGE_SIZE;
/* sg[1] for data packet, from offset */
offset = sizeof(struct padded_vnet_hdr);
sg_set_buf(&sg[1], p + offset, PAGE_SIZE - offset);
skb->data_len += PAGE_SIZE;
skb->len += PAGE_SIZE;
/* 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);
skb_shinfo(skb)->nr_frags++;
}
}
return err;
}
num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
skb_queue_head(&vi->recv, skb);
static int add_recvbuf_mergeable(struct virtnet_info *vi, gfp_t gfp)
{
struct page *page;
struct scatterlist sg;
int err;
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;
page = get_a_page(vi, gfp);
if (!page)
return -ENOMEM;
sg_init_one(&sg, page_address(page), PAGE_SIZE);
err = vi->rvq->vq_ops->add_buf(vi->rvq, &sg, 0, 1, page);
if (err < 0)
give_pages(vi, page);
return err;
}
/* 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;
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);
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);
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;
@ -407,15 +468,14 @@ 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++;
}
@ -495,9 +555,9 @@ 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);
@ -917,8 +977,7 @@ 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);
@ -953,25 +1012,35 @@ 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);