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>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/net/dst.h b/include/net/dst.h
index baf597890064..621e3513ef5e 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -110,7 +110,7 @@ struct dst_entry {
 };
 
 extern u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);
-extern const u32 dst_default_metrics[RTAX_MAX];
+extern const u32 dst_default_metrics[];
 
 #define DST_METRICS_READ_ONLY   0x1UL
 #define __DST_METRICS_PTR(Y)    \