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, 3 insertions, 3 deletions

diff --git a/net/core/dst.c b/net/core/dst.c
index 978a1ee1f7d0..32e542d7f472 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -168,7 +168,7 @@ void *dst_alloc(struct dst_ops *ops)
 {
         struct dst_entry *dst;
 
-        if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
+        if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
                 if (ops->gc(ops))
                         return NULL;
         }
@@ -183,7 +183,7 @@ void *dst_alloc(struct dst_ops *ops)
 #if RT_CACHE_DEBUG >= 2
         atomic_inc(&dst_total);
 #endif
-        atomic_inc(&ops->entries);
+        dst_entries_add(ops, 1);
         return dst;
 }
 EXPORT_SYMBOL(dst_alloc);
@@ -236,7 +236,7 @@ again:
                 neigh_release(neigh);
         }
 
-        atomic_dec(&dst->ops->entries);
+        dst_entries_add(dst->ops, -1);
 
         if (dst->ops->destroy)
                 dst->ops->destroy(dst);