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

Message ID 20130124140405.14119.49967.stgit@dragon
State Changes Requested, archived
Delegated to: David Miller
Headers show

Commit Message

Jesper Dangaard Brouer Jan. 24, 2013, 2:04 p.m.
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@redhat.com>

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

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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;