netdev - [net-next PATCH V2 1/6] net: cacheline adjust struct netns

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Message-ID: <20130129094406.13513.80799.stgit@dragon>
Date:	Tue, 29 Jan 2013 10:44:14 +0100
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Florian Westphal <fw@...len.de>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Cong Wang <amwang@...hat.com>,
	"Patrick McHardy" <kaber@...sh.net>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	Daniel Borkmann <dborkman@...hat.com>
Subject: [net-next PATCH V2 1/6] net: cacheline adjust struct netns_frags for
	better frag performance

This small cacheline adjustment of struct netns_frags improves
performance significantly for the fragmentation code.

Struct members 'lru_list' and 'mem' are both hot elements, and it
hurts performance, due to cacheline bouncing at every call point,
when they share a cacheline.  Also notice, how mem is placed
together with 'high_thresh' and 'low_thresh', as they are used in
the compare operations together.

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---

 include/net/inet_frag.h |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 32786a0..91e7797 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -3,9 +3,12 @@
 
 struct netns_frags {
 	int			nqueues;
-	atomic_t		mem;
 	struct list_head	lru_list;
 
+	/* Its important for performance to keep lru_list and mem on
+	 * separate cachelines
+	 */
+	atomic_t		mem ____cacheline_aligned_in_smp;
 	/* sysctls */
 	int			timeout;
 	int			high_thresh;

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