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authorEric Dumazet <edumazet@google.com>2012-08-07 10:55:45 +0000
committerDavid S. Miller <davem@davemloft.net>2012-08-08 16:00:28 -0700
commita37e6e344910a43b9ebc2bbf29a029f5ea942598 (patch)
tree028fe1af3e85510fa7c341bfe3dadd099189156b /net/core/dst.c
parent0c03eca3d995e73d691edea8c787e25929ec156d (diff)
downloadlinux-a37e6e344910a43b9ebc2bbf29a029f5ea942598.tar.bz2
net: force dst_default_metrics to const section
While investigating on network performance problems, I found this little gem : $ nm -v vmlinux | grep -1 dst_default_metrics ffffffff82736540 b busy.46605 ffffffff82736560 B dst_default_metrics ffffffff82736598 b dst_busy_list Apparently, declaring a const array without initializer put it in (writeable) bss section, in middle of possibly often dirtied cache lines. Since we really want dst_default_metrics be const to avoid any possible false sharing and catch any buggy writes, I force a null initializer. ffffffff818a4c20 R dst_default_metrics Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Ben Hutchings <bhutchings@solarflare.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core/dst.c')
-rw-r--r--net/core/dst.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/net/core/dst.c b/net/core/dst.c
index 069d51d29414..56d63612e1e4 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -149,7 +149,15 @@ int dst_discard(struct sk_buff *skb)
}
EXPORT_SYMBOL(dst_discard);
-const u32 dst_default_metrics[RTAX_MAX];
+const u32 dst_default_metrics[RTAX_MAX + 1] = {
+ /* This initializer is needed to force linker to place this variable
+ * into const section. Otherwise it might end into bss section.
+ * We really want to avoid false sharing on this variable, and catch
+ * any writes on it.
+ */
+ [RTAX_MAX] = 0xdeadbeef,
+};
+
void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
int initial_ref, int initial_obsolete, unsigned short flags)