Subject: [net-next PATCH 1/6] net: cacheline adjust struct netns_frags for better frag performance

From: Jesper Dangaard Brouer <[email-masked]>
Date: Thu, 24 Jan 2013 15:04:12 +0100

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 <[email-masked]>
---

 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;