fib: avoid false sharing on fib_table_hash

While doing profile analysis, I found fib_hash_table was sometime in a
cache line shared by a possibly often written kernel structure.

(CONFIG_IP_ROUTE_MULTIPATH || !CONFIG_IPV6_MULTIPLE_TABLES)

It's hard to detect because not easily reproductible.

Make sure we allocate a full cache line to keep this shared in all cpus
caches.

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

1 files changed, 6 insertions, 3 deletions

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index b6a585909d35..de382114609b 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1500,15 +1500,18 @@ static void fib6_gc_timer_cb(unsigned long arg)
 
 static int __net_init fib6_net_init(struct net *net)
 {
+        size_t size = sizeof(struct hlist_head) * FIB6_TABLE_HASHSZ;
+
         setup_timer(&net->ipv6.ip6_fib_timer, fib6_gc_timer_cb, (unsigned long)net);
 
         net->ipv6.rt6_stats = kzalloc(sizeof(*net->ipv6.rt6_stats), GFP_KERNEL);
         if (!net->ipv6.rt6_stats)
                 goto out_timer;
 
-        net->ipv6.fib_table_hash = kcalloc(FIB6_TABLE_HASHSZ,
-                                           sizeof(*net->ipv6.fib_table_hash),
-                                           GFP_KERNEL);
+        /* Avoid false sharing : Use at least a full cache line */
+        size = max_t(size_t, size, L1_CACHE_BYTES);
+
+        net->ipv6.fib_table_hash = kzalloc(size, GFP_KERNEL);
         if (!net->ipv6.fib_table_hash)
                 goto out_rt6_stats;