* [PATCH net-next] net: output path optimizations
@ 2012-08-07 12:19 Eric Dumazet
2012-08-07 23:26 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Eric Dumazet @ 2012-08-07 12:19 UTC (permalink / raw)
To: David Miller; +Cc: netdev
From: Eric Dumazet <edumazet@google.com>
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>
---
include/net/dst.h | 10 +++++++---
include/net/neighbour.h | 14 +++++++++-----
2 files changed, 16 insertions(+), 8 deletions(-)
diff --git a/include/net/dst.h b/include/net/dst.h
index baf5978..77f52f7 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -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;
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 @@ 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);
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH net-next] net: output path optimizations
2012-08-07 12:19 [PATCH net-next] net: output path optimizations Eric Dumazet
@ 2012-08-07 23:26 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2012-08-07 23:26 UTC (permalink / raw)
To: eric.dumazet; +Cc: netdev
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 07 Aug 2012 14:19:56 +0200
> From: Eric Dumazet <edumazet@google.com>
>
> 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>
Applied, I'd like to significantly redo how the neigh confirmation
stuff works.
I'm not at all surprised it shows up on TCP workloads.
^ permalink raw reply [flat|nested] 2+ messages in thread
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