net dst: use a percpu_counter to track entries

struct dst_ops tracks number of allocated dst in an atomic_t field,
subject to high cache line contention in stress workload.

Switch to a percpu_counter, to reduce number of time we need to dirty a
central location. Place it on a separate cache line to avoid dirtying
read only fields.

Stress test :

(Sending 160.000.000 UDP frames,
IP route cache disabled, dual E5540 @2.53GHz,
32bit kernel, FIB_TRIE, SLUB/NUMA)

Before:

real    0m51.179s
user    0m15.329s
sys     10m15.942s

After:

real	0m45.570s
user	0m15.525s
sys	9m56.669s

With a small reordering of struct neighbour fields, subject of a
following patch, (to separate refcnt from other read mostly fields)

real	0m41.841s
user	0m15.261s
sys	8m45.949s

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/ipv4/xfrm4_policy.c b/net/ipv4/xfrm4_policy.c
index a580349f0b8a..4464f3bff6a7 100644
--- a/net/ipv4/xfrm4_policy.c
+++ b/net/ipv4/xfrm4_policy.c
@@ -174,7 +174,7 @@ static inline int xfrm4_garbage_collect(struct dst_ops *ops)
 	struct net *net = container_of(ops, struct net, xfrm.xfrm4_dst_ops);
 
 	xfrm4_policy_afinfo.garbage_collect(net);
-	return (atomic_read(&ops->entries) > ops->gc_thresh * 2);
+	return (dst_entries_get_slow(ops) > ops->gc_thresh * 2);
 }
 
 static void xfrm4_update_pmtu(struct dst_entry *dst, u32 mtu)
@@ -232,7 +232,6 @@ static struct dst_ops xfrm4_dst_ops = {
 	.ifdown =		xfrm4_dst_ifdown,
 	.local_out =		__ip_local_out,
 	.gc_thresh =		1024,
-	.entries =		ATOMIC_INIT(0),
 };
 
 static struct xfrm_policy_afinfo xfrm4_policy_afinfo = {
@@ -288,6 +287,7 @@ void __init xfrm4_init(int rt_max_size)
 	 * and start cleaning when were 1/2 full
 	 */
 	xfrm4_dst_ops.gc_thresh = rt_max_size/2;
+	dst_entries_init(&xfrm4_dst_ops);
 
 	xfrm4_state_init();
 	xfrm4_policy_init();