fib: introduce fib_alias_accessed() helper
Perf tools session at NFWS 2010 pointed out a false sharing on struct
fib_alias that can be avoided pretty easily, if we set FA_S_ACCESSED bit
only if needed (ie : not already set)
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/fib_lookup.h b/net/ipv4/fib_lookup.h
index 5072d8e..a29edf2 100644
--- a/net/ipv4/fib_lookup.h
+++ b/net/ipv4/fib_lookup.h
@@ -17,6 +17,13 @@
#define FA_S_ACCESSED 0x01
+/* Dont write on fa_state unless needed, to keep it shared on all cpus */
+static inline void fib_alias_accessed(struct fib_alias *fa)
+{
+ if (!(fa->fa_state & FA_S_ACCESSED))
+ fa->fa_state |= FA_S_ACCESSED;
+}
+
/* Exported by fib_semantics.c */
extern int fib_semantic_match(struct list_head *head,
const struct flowi *flp,