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, 20 insertions, 8 deletions

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 17e217933885..25661f968f3f 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -109,7 +109,6 @@ static struct dst_ops ip6_dst_ops_template = {
         .link_failure           =       ip6_link_failure,
         .update_pmtu            =       ip6_rt_update_pmtu,
         .local_out              =       __ip6_local_out,
-        .entries                =       ATOMIC_INIT(0),
 };
 
 static void ip6_rt_blackhole_update_pmtu(struct dst_entry *dst, u32 mtu)
@@ -122,7 +121,6 @@ static struct dst_ops ip6_dst_blackhole_ops = {
         .destroy                =       ip6_dst_destroy,
         .check                  =       ip6_dst_check,
         .update_pmtu            =       ip6_rt_blackhole_update_pmtu,
-        .entries                =       ATOMIC_INIT(0),
 };
 
 static struct rt6_info ip6_null_entry_template = {
@@ -1058,19 +1056,22 @@ static int ip6_dst_gc(struct dst_ops *ops)
         int rt_elasticity = net->ipv6.sysctl.ip6_rt_gc_elasticity;
         int rt_gc_timeout = net->ipv6.sysctl.ip6_rt_gc_timeout;
         unsigned long rt_last_gc = net->ipv6.ip6_rt_last_gc;
+        int entries;
 
+        entries = dst_entries_get_fast(ops);
         if (time_after(rt_last_gc + rt_min_interval, now) &&
-            atomic_read(&ops->entries) <= rt_max_size)
+            entries <= rt_max_size)
                 goto out;
 
         net->ipv6.ip6_rt_gc_expire++;
         fib6_run_gc(net->ipv6.ip6_rt_gc_expire, net);
         net->ipv6.ip6_rt_last_gc = now;
-        if (atomic_read(&ops->entries) < ops->gc_thresh)
+        entries = dst_entries_get_slow(ops);
+        if (entries < ops->gc_thresh)
                 net->ipv6.ip6_rt_gc_expire = rt_gc_timeout>>1;
 out:
         net->ipv6.ip6_rt_gc_expire -= net->ipv6.ip6_rt_gc_expire>>rt_elasticity;
-        return atomic_read(&ops->entries) > rt_max_size;
+        return entries > rt_max_size;
 }
 
 /* Clean host part of a prefix. Not necessary in radix tree,
@@ -2524,7 +2525,7 @@ static int rt6_stats_seq_show(struct seq_file *seq, void *v)
                    net->ipv6.rt6_stats->fib_rt_alloc,
                    net->ipv6.rt6_stats->fib_rt_entries,
                    net->ipv6.rt6_stats->fib_rt_cache,
-                   atomic_read(&net->ipv6.ip6_dst_ops.entries),
+                   dst_entries_get_slow(&net->ipv6.ip6_dst_ops),
                    net->ipv6.rt6_stats->fib_discarded_routes);
 
         return 0;
@@ -2666,11 +2667,14 @@ static int __net_init ip6_route_net_init(struct net *net)
         memcpy(&net->ipv6.ip6_dst_ops, &ip6_dst_ops_template,
                sizeof(net->ipv6.ip6_dst_ops));
 
+        if (dst_entries_init(&net->ipv6.ip6_dst_ops) < 0)
+                goto out_ip6_dst_ops;
+
         net->ipv6.ip6_null_entry = kmemdup(&ip6_null_entry_template,
                                            sizeof(*net->ipv6.ip6_null_entry),
                                            GFP_KERNEL);
         if (!net->ipv6.ip6_null_entry)
-                goto out_ip6_dst_ops;
+                goto out_ip6_dst_entries;
         net->ipv6.ip6_null_entry->dst.path =
                 (struct dst_entry *)net->ipv6.ip6_null_entry;
         net->ipv6.ip6_null_entry->dst.ops = &net->ipv6.ip6_dst_ops;
@@ -2720,6 +2724,8 @@ out_ip6_prohibit_entry:
 out_ip6_null_entry:
         kfree(net->ipv6.ip6_null_entry);
 #endif
+out_ip6_dst_entries:
+        dst_entries_destroy(&net->ipv6.ip6_dst_ops);
 out_ip6_dst_ops:
         goto out;
 }
@@ -2758,10 +2764,14 @@ int __init ip6_route_init(void)
         if (!ip6_dst_ops_template.kmem_cachep)
                 goto out;
 
-        ret = register_pernet_subsys(&ip6_route_net_ops);
+        ret = dst_entries_init(&ip6_dst_blackhole_ops);
         if (ret)
                 goto out_kmem_cache;
 
+        ret = register_pernet_subsys(&ip6_route_net_ops);
+        if (ret)
+                goto out_dst_entries;
+
         ip6_dst_blackhole_ops.kmem_cachep = ip6_dst_ops_template.kmem_cachep;
 
         /* Registering of the loopback is done before this portion of code,
@@ -2808,6 +2818,8 @@ out_fib6_init:
         fib6_gc_cleanup();
 out_register_subsys:
         unregister_pernet_subsys(&ip6_route_net_ops);
+out_dst_entries:
+        dst_entries_destroy(&ip6_dst_blackhole_ops);
 out_kmem_cache:
         kmem_cache_destroy(ip6_dst_ops_template.kmem_cachep);
         goto out;