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@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 32786a0..91e7797 100644 (file)
--- 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;