From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH net-next] fib: introduce fib_alias_accessed() helper Date: Thu, 21 Oct 2010 10:03:38 +0200 Message-ID: <1287648218.6871.18.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-f44.google.com ([74.125.82.44]:44020 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751282Ab0JUIDm (ORCPT ); Thu, 21 Oct 2010 04:03:42 -0400 Received: by wwf26 with SMTP id 26so2244769wwf.1 for ; Thu, 21 Oct 2010 01:03:41 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Perf tools session at NFWS 2010 pointed out a false sharing on struct fib_alias that can be avoided pretty easily, if we set FA_S_ACCESSED bit only if needed (ie : not already set) Signed-off-by: Eric Dumazet --- net/ipv4/fib_hash.c | 3 ++- net/ipv4/fib_lookup.h | 7 +++++++ net/ipv4/fib_semantics.c | 2 +- net/ipv4/fib_trie.c | 3 ++- 4 files changed, 12 insertions(+), 3 deletions(-) diff --git a/net/ipv4/fib_hash.c b/net/ipv4/fib_hash.c index 4f1aafd..43e1c59 100644 --- a/net/ipv4/fib_hash.c +++ b/net/ipv4/fib_hash.c @@ -335,7 +335,8 @@ void fib_table_select_default(struct fib_table *tb, if (!next_fi->fib_nh[0].nh_gw || next_fi->fib_nh[0].nh_scope != RT_SCOPE_LINK) continue; - fa->fa_state |= FA_S_ACCESSED; + + fib_alias_accessed(fa); if (fi == NULL) { if (next_fi != res->fi) diff --git a/net/ipv4/fib_lookup.h b/net/ipv4/fib_lookup.h index 5072d8e..a29edf2 100644 --- a/net/ipv4/fib_lookup.h +++ b/net/ipv4/fib_lookup.h @@ -17,6 +17,13 @@ struct fib_alias { #define FA_S_ACCESSED 0x01 +/* Dont write on fa_state unless needed, to keep it shared on all cpus */ +static inline void fib_alias_accessed(struct fib_alias *fa) +{ + if (!(fa->fa_state & FA_S_ACCESSED)) + fa->fa_state |= FA_S_ACCESSED; +} + /* Exported by fib_semantics.c */ extern int fib_semantic_match(struct list_head *head, const struct flowi *flp, diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index 6734c9c..3e0da3e 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -901,7 +901,7 @@ int fib_semantic_match(struct list_head *head, const struct flowi *flp, if (fa->fa_scope < flp->fl4_scope) continue; - fa->fa_state |= FA_S_ACCESSED; + fib_alias_accessed(fa); err = fib_props[fa->fa_type].error; if (err == 0) { diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 31494f3..cd5e13a 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -1838,7 +1838,8 @@ void fib_table_select_default(struct fib_table *tb, if (!next_fi->fib_nh[0].nh_gw || next_fi->fib_nh[0].nh_scope != RT_SCOPE_LINK) continue; - fa->fa_state |= FA_S_ACCESSED; + + fib_alias_accessed(fa); if (fi == NULL) { if (next_fi != res->fi)