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| author | Eric Dumazet <edumazet@google.com> | 2012-08-07 12:55:45 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2012-08-09 01:00:28 +0200 |
| commit | a37e6e344910a43b9ebc2bbf29a029f5ea942598 (patch) | |
| tree | 028fe1af3e85510fa7c341bfe3dadd099189156b | |
| parent | net: fib: fix incorrect call_rcu_bh() (diff) | |
| download | linux-a37e6e344910a43b9ebc2bbf29a029f5ea942598.tar.xz linux-a37e6e344910a43b9ebc2bbf29a029f5ea942598.zip | |
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>
| -rw-r--r-- | include/net/dst.h | 2 | ||||
| -rw-r--r-- | net/core/dst.c | 10 |
2 files changed, 10 insertions, 2 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) \ 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) |