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, 5 insertions, 6 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 919f2ad19b49..3df057e89640 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -1016,16 +1016,15 @@ static struct notifier_block fib_netdev_notifier = {
 static int __net_init ip_fib_net_init(struct net *net)
 {
         int err;
-        unsigned int i;
+        size_t size = sizeof(struct hlist_head) * FIB_TABLE_HASHSZ;
+
+        /* Avoid false sharing : Use at least a full cache line */
+        size = max_t(size_t, size, L1_CACHE_BYTES);
 
-        net->ipv4.fib_table_hash = kzalloc(
-                        sizeof(struct hlist_head)*FIB_TABLE_HASHSZ, GFP_KERNEL);
+        net->ipv4.fib_table_hash = kzalloc(size, GFP_KERNEL);
         if (net->ipv4.fib_table_hash == NULL)
                 return -ENOMEM;
 
-        for (i = 0; i < FIB_TABLE_HASHSZ; i++)
-                INIT_HLIST_HEAD(&net->ipv4.fib_table_hash[i]);
-
         err = fib4_rules_init(net);
         if (err < 0)
                 goto fail;