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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>
This commit is contained in:
Eric Dumazet 2012-08-07 02:19:56 +00:00 committed by David S. Miller
parent e07b94f135
commit 425f09ab7d
2 changed files with 16 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/net/dst.h
View File

@ -396,11 +396,15 @@ static inline void dst_confirm(struct dst_entry *dst)
static inline int dst_neigh_output(struct dst_entry *dst, struct neighbour *n,
struct sk_buff *skb)
{
struct hh_cache *hh;
const struct hh_cache *hh;
if (dst->pending_confirm) {
unsigned long now = jiffies;
if (unlikely(dst->pending_confirm)) {
n->confirmed = jiffies;
dst->pending_confirm = 0;
/* avoid dirtying neighbour */
if (n->confirmed != now)
n->confirmed = now;
}
hh = &n->hh;

14
include/net/neighbour.h
View File

@ -334,18 +334,22 @@ static inline int neigh_hh_bridge(struct hh_cache *hh, struct sk_buff *skb)
}
#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);