From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH net-next] fib: avoid false sharing on fib_table_hash Date: Wed, 13 Oct 2010 20:22:03 +0200 Message-ID: <1286994123.3876.1137.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev To: David Miller Return-path: Received: from mail-ww0-f42.google.com ([74.125.82.42]:48666 "EHLO mail-ww0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751363Ab0JMSWv (ORCPT ); Wed, 13 Oct 2010 14:22:51 -0400 Received: by wwi14 with SMTP id 14so175021wwi.1 for ; Wed, 13 Oct 2010 11:22:18 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: 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 --- We probably need a generic kernel function, but it might take time... net/ipv4/fib_frontend.c | 11 +++++------ net/ipv6/ip6_fib.c | 9 ++++++--- 2 files changed, 11 insertions(+), 9 deletions(-) diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c index 919f2ad..3df057e 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; diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index b6a5859..de38211 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;