* [PATCH 2/2] virtio_net: Defer skb allocation in receive path Date: Wed, 13 Jan 2010 12:53:38 -0800
2010-01-29 13:19 ` [PATCH 1/2] virtio: Add ability to detach unused buffers from vrings Rusty Russell
@ 2010-01-29 13:20 ` Rusty Russell
2010-02-02 23:59 ` David Miller
2010-02-02 23:59 ` [PATCH 1/2] virtio: Add ability to detach unused buffers from vrings David Miller
1 sibling, 1 reply; 7+ messages in thread
From: Rusty Russell @ 2010-01-29 13:20 UTC (permalink / raw)
To: netdev; +Cc: David Miller, virtualization, Shirley Ma, Michael S. Tsirkin
From: Shirley Ma <mashirle@us.ibm.com>
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>
---
drivers/net/virtio_net.c | 427 +++++++++++++++++++++++++++--------------------
1 file 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);
^ permalink raw reply related [flat|nested] 7+ messages in thread