gro: Avoid copying headers of unmerged packets
Unfortunately simplicity isn't always the best. The fraginfo
interface turned out to be suboptimal. The problem was quite
obvious. For every packet, we have to copy the headers from
the frags structure into skb->head, even though for 99% of the
packets this part is immediately thrown away after the merge.
LRO didn't have this problem because it directly read the headers
from the frags structure.
This patch attempts to address this by creating an interface
that allows GRO to access the headers in the first frag without
having to copy it. Because all drivers that use frags place the
headers in the first frag this optimisation should be enough.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index cd23ae1..df406dc 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -215,6 +215,13 @@
return &net->dev_index_head[ifindex & ((1 << NETDEV_HASHBITS) - 1)];
}
+static inline void *skb_gro_mac_header(struct sk_buff *skb)
+{
+ return skb_headlen(skb) ? skb_mac_header(skb) :
+ page_address(skb_shinfo(skb)->frags[0].page) +
+ skb_shinfo(skb)->frags[0].page_offset;
+}
+
/* Device list insertion */
static int list_netdevice(struct net_device *dev)
{
@@ -2350,7 +2357,6 @@
out:
skb_shinfo(skb)->gso_size = 0;
- __skb_push(skb, -skb_network_offset(skb));
return netif_receive_skb(skb);
}
@@ -2368,6 +2374,25 @@
}
EXPORT_SYMBOL(napi_gro_flush);
+void *skb_gro_header(struct sk_buff *skb, unsigned int hlen)
+{
+ unsigned int offset = skb_gro_offset(skb);
+
+ hlen += offset;
+ if (hlen <= skb_headlen(skb))
+ return skb->data + offset;
+
+ if (unlikely(!skb_shinfo(skb)->nr_frags ||
+ skb_shinfo(skb)->frags[0].size <=
+ hlen - skb_headlen(skb) ||
+ PageHighMem(skb_shinfo(skb)->frags[0].page)))
+ return pskb_may_pull(skb, hlen) ? skb->data + offset : NULL;
+
+ return page_address(skb_shinfo(skb)->frags[0].page) +
+ skb_shinfo(skb)->frags[0].page_offset + offset;
+}
+EXPORT_SYMBOL(skb_gro_header);
+
int dev_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
{
struct sk_buff **pp = NULL;
@@ -2388,11 +2413,13 @@
rcu_read_lock();
list_for_each_entry_rcu(ptype, head, list) {
struct sk_buff *p;
+ void *mac;
if (ptype->type != type || ptype->dev || !ptype->gro_receive)
continue;
- skb_reset_network_header(skb);
+ skb_set_network_header(skb, skb_gro_offset(skb));
+ mac = skb_gro_mac_header(skb);
mac_len = skb->network_header - skb->mac_header;
skb->mac_len = mac_len;
NAPI_GRO_CB(skb)->same_flow = 0;
@@ -2406,8 +2433,7 @@
continue;
if (p->mac_len != mac_len ||
- memcmp(skb_mac_header(p), skb_mac_header(skb),
- mac_len))
+ memcmp(skb_mac_header(p), mac, mac_len))
NAPI_GRO_CB(p)->same_flow = 0;
}
@@ -2434,13 +2460,11 @@
if (same_flow)
goto ok;
- if (NAPI_GRO_CB(skb)->flush || count >= MAX_GRO_SKBS) {
- __skb_push(skb, -skb_network_offset(skb));
+ if (NAPI_GRO_CB(skb)->flush || count >= MAX_GRO_SKBS)
goto normal;
- }
NAPI_GRO_CB(skb)->count = 1;
- skb_shinfo(skb)->gso_size = skb->len;
+ skb_shinfo(skb)->gso_size = skb_gro_len(skb);
skb->next = napi->gro_list;
napi->gro_list = skb;
ret = GRO_HELD;
@@ -2488,6 +2512,8 @@
int napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
{
+ skb_gro_reset_offset(skb);
+
return napi_skb_finish(__napi_gro_receive(napi, skb), skb);
}
EXPORT_SYMBOL(napi_gro_receive);
@@ -2506,6 +2532,7 @@
{
struct net_device *dev = napi->dev;
struct sk_buff *skb = napi->skb;
+ struct ethhdr *eth;
napi->skb = NULL;
@@ -2525,13 +2552,23 @@
skb->len += info->len;
skb->truesize += info->len;
- if (!pskb_may_pull(skb, ETH_HLEN)) {
+ skb_reset_mac_header(skb);
+ skb_gro_reset_offset(skb);
+
+ eth = skb_gro_header(skb, sizeof(*eth));
+ if (!eth) {
napi_reuse_skb(napi, skb);
skb = NULL;
goto out;
}
- skb->protocol = eth_type_trans(skb, dev);
+ skb_gro_pull(skb, sizeof(*eth));
+
+ /*
+ * This works because the only protocols we care about don't require
+ * special handling. We'll fix it up properly at the end.
+ */
+ skb->protocol = eth->h_proto;
skb->ip_summed = info->ip_summed;
skb->csum = info->csum;
@@ -2544,10 +2581,21 @@
int napi_frags_finish(struct napi_struct *napi, struct sk_buff *skb, int ret)
{
int err = NET_RX_SUCCESS;
+ int may;
switch (ret) {
case GRO_NORMAL:
- return netif_receive_skb(skb);
+ case GRO_HELD:
+ may = pskb_may_pull(skb, skb_gro_offset(skb));
+ BUG_ON(!may);
+
+ skb->protocol = eth_type_trans(skb, napi->dev);
+
+ if (ret == GRO_NORMAL)
+ return netif_receive_skb(skb);
+
+ skb_gro_pull(skb, -ETH_HLEN);
+ break;
case GRO_DROP:
err = NET_RX_DROP;