[PATCH v2 2/4] Defer skb allocation -- new skb_set calls & chain pages in virtio_net

Shirley Ma
2009-12-11T12:43:02Z

Signed-off-by: Shirley Ma <xma@us.ibm.com>
--------------

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index bb5eb7b..100b4b9 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -80,29 +80,25 @@ 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)
+static void give_pages(struct virtnet_info *vi, struct page *page)
{
- page->private = (unsigned long)vi->pages;
- vi->pages = page;
-}
+ struct page *end;

-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;
+ /* 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
+ /* use private to chain pages for big packets */
+ p->private = 0;
+ } else
p = alloc_page(gfp_mask);
return p;
}
@@ -128,6 +124,85 @@ static void skb_xmit_done(struct virtqueue *svq)
netif_wake_queue(vi->dev);
}

+static int skb_set_frag(struct sk_buff *skb, struct page *page,
+ int offset, int len)
+{
+ int i = skb_shinfo(skb)->nr_frags;
+ skb_frag_t *f;
+
+ i = skb_shinfo(skb)->nr_frags;
+ f = &skb_shinfo(skb)->frags[i];
+ f->page = page;
+ f->page_offset = offset;
+
+ if (len > PAGE_SIZE - f->page_offset)
+ f->size = PAGE_SIZE - f->page_offset;
+ else
+ f->size = len;
+
+ skb_shinfo(skb)->nr_frags++;
+ skb->data_len += f->size;
+ skb->len += f->size;
+
+ len -= f->size;
+ return len;
+}
+
+static struct sk_buff *skb_goodcopy(struct virtnet_info *vi, struct page **page,
+ unsigned int *len)
+{
+ struct sk_buff *skb;
+ struct skb_vnet_hdr *hdr;
+ int copy, hdr_len, offset;
+ char *p;
+
+ p = page_address(*page);
+
+ skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN);
+ if (unlikely(!skb))
+ return NULL;
+
+ skb_reserve(skb, NET_IP_ALIGN);
+ hdr = skb_vnet_hdr(skb);
+
+ if (vi->mergeable_rx_bufs) {
+ hdr_len = sizeof(hdr->mhdr);
+ offset = hdr_len;
+ } else {
+ /* share one page between virtio_net header and data */
+ struct padded_vnet_hdr {
+ struct virtio_net_hdr hdr;
+ /* This padding makes our data 16 byte aligned */
+ char padding[6];
+ };
+ 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;
+
+ if (*len) {
+ *len = skb_set_frag(skb, *page, offset, *len);
+ *page = (struct page *)(*page)->private;
+ } else {
+ give_pages(vi, *page);
+ *page = NULL;
+ }
+
+ return skb;
+}
+
static void receive_skb(struct net_device *dev, struct sk_buff *skb,
unsigned len)
{
@@ -162,7 +237,7 @@ 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);
+ give_pages(vi, skb_shinfo(skb)->frags[0].page);
skb_shinfo(skb)->nr_frags--;
} else {
skb_shinfo(skb)->frags[0].page_offset +=