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Commit 10da66f7 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 874ffa8f

net/ipv4/fib_frontend.c

+5 −6
Original line number Diff line number Diff line
@@ -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;

net/ipv6/ip6_fib.c

+6 −3
Original line number Diff line number Diff line
@@ -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;