net: output path optimizations
1) Avoid dirtying neighbour's confirmed field.
TCP workloads hits this cache line for each incoming ACK.
Lets write n->confirmed only if there is a jiffie change.
2) Optimize neigh_hh_output() for the common Ethernet case, were
hh_len is less than 16 bytes. Replace the memcpy() call
by two inlined 64bit load/stores on x86_64.
Bench results using udpflood test, with -C option (MSG_CONFIRM flag
added to sendto(), to reproduce the n->confirmed dirtying on UDP)
24 threads doing 1.000.000 UDP sendto() on dummy device, 4 runs.
before : 2.247s, 2.235s, 2.247s, 2.318s
after : 1.884s, 1.905s, 1.891s, 1.895s
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 344d898..0dab173 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -334,18 +334,22 @@
}
#endif
-static inline int neigh_hh_output(struct hh_cache *hh, struct sk_buff *skb)
+static inline int neigh_hh_output(const struct hh_cache *hh, struct sk_buff *skb)
{
unsigned int seq;
int hh_len;
do {
- int hh_alen;
-
seq = read_seqbegin(&hh->hh_lock);
hh_len = hh->hh_len;
- hh_alen = HH_DATA_ALIGN(hh_len);
- memcpy(skb->data - hh_alen, hh->hh_data, hh_alen);
+ if (likely(hh_len <= HH_DATA_MOD)) {
+ /* this is inlined by gcc */
+ memcpy(skb->data - HH_DATA_MOD, hh->hh_data, HH_DATA_MOD);
+ } else {
+ int hh_alen = HH_DATA_ALIGN(hh_len);
+
+ memcpy(skb->data - hh_alen, hh->hh_data, hh_alen);
+ }
} while (read_seqretry(&hh->hh_lock, seq));
skb_push(skb, hh_len);