Guest 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 it when it's useless.
This patch has deferred skb allocation to when receiving packets,
it reduces skb pre-allocations and skb_frees. And it induces two
page list: freed_pages and used_page list, used_pages is used to
track pages pre-allocated, it is only useful when removing virtio_net.
This patch has tested and measured against 2.6.31-rc4 git,
I thought this patch will improve large packet performance, but I saw
netperf TCP_STREAM performance improved for small packet for both
local guest to host and host to local guest cases. It also reduces
UDP packets drop rate from host to local guest. I am not fully understand
why.
The netperf results from my laptop are:
mtu=1500
netperf -H xxx -l 120
w/o patch w/i patch (two runs)
guest to host: 3336.84Mb/s 3730.14Mb/s ~ 3582.88Mb/s
host to guest: 3165.10Mb/s 3370.39Mb/s ~ 3407.96Mb/s
Here is the patch for your review. The same approach can apply to non-mergable
buffs too, so we can use code in common. If there is no objection, I will
submit the non-mergable buffs patch later.
Signed-off-by: Shirley Ma <xma@xxxxxxxxxx>
---
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 2a6e81d..e31ebc9 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -17,6 +17,7 @@
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
//#define DEBUG
+#include <linux/list.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/ethtool.h>
@@ -39,6 +40,12 @@ module_param(gso, bool, 0444);
#define VIRTNET_SEND_COMMAND_SG_MAX 2
+struct page_list
+{
+ struct page *page;
+ struct list_head list;
+};
+
struct virtnet_info
{
struct virtio_device *vdev;
@@ -72,6 +79,8 @@ struct virtnet_info
/* Chain pages by the private ptr. */
struct page *pages;
+ struct list_head used_pages;
+ struct list_head freed_pages;
};
static inline void *skb_vnet_hdr(struct sk_buff *skb)
@@ -106,6 +115,26 @@ static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
return p;
}
+static struct page_list *get_a_free_page(struct virtnet_info *vi, gfp_t gfp_mask)
+{
+ struct page_list *plist;
+
+ if (list_empty(&vi->freed_pages)) {
+ plist = kmalloc(sizeof(struct page_list), gfp_mask);
+ if (!plist)
+ return NULL;
+ list_add_tail(&plist->list, &vi->freed_pages);
+ plist->page = alloc_page(gfp_mask);
+ } else {
+ plist = list_first_entry(&vi->freed_pages, struct page_list, list);
+ if (!plist->page)
+ plist->page = alloc_page(gfp_mask);
+ }
+ if (plist->page)
+ list_move_tail(&plist->list, &vi->used_pages);
+ return plist;
+}
+
static void skb_xmit_done(struct virtqueue *svq)
{
struct virtnet_info *vi = svq->vdev->priv;
@@ -121,14 +150,14 @@ static void skb_xmit_done(struct virtqueue *svq)
tasklet_schedule(&vi->tasklet);
}
-static void receive_skb(struct net_device *dev, struct sk_buff *skb,
+static void receive_skb(struct net_device *dev, void *buf,
unsigned len)
{
struct virtnet_info *vi = netdev_priv(dev);
- struct virtio_net_hdr *hdr = skb_vnet_hdr(skb);
int err;
int i;
-
+ struct sk_buff *skb = NULL;
+ struct virtio_net_hdr *hdr = NULL;
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++;
@@ -136,15 +165,30 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb,
}
if (vi->mergeable_rx_bufs) {
- struct virtio_net_hdr_mrg_rxbuf *mhdr = skb_vnet_hdr(skb);
+ struct virtio_net_hdr_mrg_rxbuf *mhdr;
unsigned int copy;
- char *p = page_address(skb_shinfo(skb)->frags[0].page);
+ skb_frag_t *f;
+ struct page_list *plist = (struct page_list *)buf;
+ char *p = page_address(plist->page);
+
+ skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN);
+ if (unlikely(!skb)) {
+ /* drop the packet */
+ dev->stats.rx_dropped++;
+ list_move_tail(&plist->list, &vi->freed_pages);
+ return;
+ }
+
+ skb_reserve(skb, NET_IP_ALIGN);
if (len > PAGE_SIZE)
len = PAGE_SIZE;
len -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
- memcpy(hdr, p, sizeof(*mhdr));
+ mhdr = skb_vnet_hdr(skb);
+ memcpy(mhdr, p, sizeof(*mhdr));
+ hdr = (struct virtio_net_hdr *)mhdr;
+
p += sizeof(*mhdr);
copy = len;
@@ -155,20 +199,20 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb,
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 +=
+ if (len) {
+ f = &skb_shinfo(skb)->frags[0];
+ f->page = plist->page;
+ skb_shinfo(skb)->frags[0].page_offset =
sizeof(*mhdr) + copy;
skb_shinfo(skb)->frags[0].size = len;
skb->data_len += len;
skb->len += len;
+ skb_shinfo(skb)->nr_frags++;
+ plist->page = NULL;
}
+ list_move_tail(&plist->list, &vi->freed_pages);
while (--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,
@@ -177,30 +221,30 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb,
goto drop;
}
- nskb = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
- if (!nskb) {
+ plist = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
+ if (!plist) {
pr_debug("%s: rx error: %d buffers missing\n",
dev->name, 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);
-
+ f = &skb_shinfo(skb)->frags[i];
+ f->page = plist->page;
+ f->page_offset = 0;
+
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;
+ plist->page = NULL;
+ list_move_tail(&plist->list, &vi->freed_pages);
}
} else {
+ skb = (struct sk_buff *)buf;
+ hdr = skb_vnet_hdr(skb);
len -= sizeof(struct virtio_net_hdr);
if (len <= MAX_PACKET_LEN)
@@ -329,7 +373,6 @@ static void try_fill_recv_maxbufs(struct virtnet_info *vi)
static void try_fill_recv(struct virtnet_info *vi)
{
- struct sk_buff *skb;
struct scatterlist sg[1];
int err;
@@ -339,39 +382,21 @@ static void try_fill_recv(struct virtnet_info *vi)
}
for (;;) {
- skb_frag_t *f;
-
- skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN);
- if (unlikely(!skb))
- break;
-
- skb_reserve(skb, NET_IP_ALIGN);
-
- f = &skb_shinfo(skb)->frags[0];
- f->page = get_a_page(vi, GFP_ATOMIC);
- if (!f->page) {
- kfree_skb(skb);
+ struct page_list *plist = get_a_free_page(vi, GFP_ATOMIC);
+ if (!plist || !plist->page)
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);
+ sg_init_one(sg, page_address(plist->page), PAGE_SIZE);
+ err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, plist);
if (err) {
- skb_unlink(skb, &vi->recv);
- kfree_skb(skb);
+ list_move_tail(&plist->list, &vi->freed_pages);
break;
}
vi->num++;
}
+
if (unlikely(vi->num > vi->max))
vi->max = vi->num;
+
vi->rvq->vq_ops->kick(vi->rvq);
}
@@ -388,14 +413,15 @@ static void skb_recv_done(struct virtqueue *rvq)
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) {
+ if (!vi->mergeable_rx_bufs)
+ __skb_unlink((struct sk_buff *)buf, &vi->recv);
+ receive_skb(vi->dev, buf, len);
vi->num--;
received++;
}
@@ -893,6 +919,8 @@ static int virtnet_probe(struct virtio_device *vdev)
vi->vdev = vdev;
vdev->priv = vi;
vi->pages = NULL;
+ INIT_LIST_HEAD(&vi->used_pages);
+ INIT_LIST_HEAD(&vi->freed_pages);
/* If they give us a callback when all buffers are done, we don't need
* the timer. */
@@ -969,6 +997,7 @@ static void virtnet_remove(struct virtio_device *vdev)
{
struct virtnet_info *vi = vdev->priv;
struct sk_buff *skb;
+ struct page_list *plist, *tp;
/* Stop all the virtqueues. */
vdev->config->reset(vdev);
@@ -977,14 +1006,23 @@ static void virtnet_remove(struct virtio_device *vdev)
del_timer_sync(&vi->xmit_free_timer);
/* Free our skbs in send and recv queues, if any. */
- while ((skb = __skb_dequeue(&vi->recv)) != NULL) {
- kfree_skb(skb);
- vi->num--;
+ if (!vi->mergeable_rx_bufs) {
+ while ((skb = __skb_dequeue(&vi->recv)) != NULL) {
+ kfree_skb(skb);
+ vi->num--;
+ }
+ BUG_ON(vi->num != 0);
+ } else {
+ list_splice_init(&vi->used_pages, &vi->freed_pages);
+ list_for_each_entry_safe(plist, tp, &vi->freed_pages, list) {
+ vi->num--;
+ if (plist->page)
+ __free_pages(plist->page, 0);
+ kfree(plist);
+ }
}
__skb_queue_purge(&vi->send);
- BUG_ON(vi->num != 0);
-
unregister_netdev(vi->dev);
vdev->config->del_vqs(vi->vdev);
--
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