diff mbox

[v3,2/9] rhashtable: Eliminate unnecessary branch in rht_key_hashfn

Message ID E1Ya2kG-0004HI-9N@gondolin.me.apana.org.au
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Herbert Xu March 23, 2015, 1:50 p.m. UTC
When rht_key_hashfn is called from rhashtable itself and params
is equal to ht->p, there is no point in checking params.key_len
and falling back to ht->p.key_len.

For some reason gcc couldn't figure out that params is the same
as ht->p.  So let's help it by only checking params.key_len when
it's a constant.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---

 include/linux/rhashtable.h |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Comments

Thomas Graf March 23, 2015, 1:58 p.m. UTC | #1
On 03/24/15 at 12:50am, Herbert Xu wrote:
> When rht_key_hashfn is called from rhashtable itself and params
> is equal to ht->p, there is no point in checking params.key_len
> and falling back to ht->p.key_len.
> 
> For some reason gcc couldn't figure out that params is the same
> as ht->p.  So let's help it by only checking params.key_len when
> it's a constant.
> 
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Acked-by: Thomas Graf <tgraf@suug.ch>
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
diff mbox

Patch

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 18a6488..e316f10 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -199,8 +199,12 @@  static inline unsigned int rht_key_hashfn(
 	struct rhashtable *ht, const struct bucket_table *tbl,
 	const void *key, const struct rhashtable_params params)
 {
-	return rht_bucket_index(tbl, params.hashfn(key, params.key_len ?:
-							ht->p.key_len,
+	/* params must be equal to ht->p if it isn't constant. */
+	unsigned key_len = __builtin_constant_p(params.key_len) ?
+			   (params.key_len ?: ht->p.key_len) :
+			   params.key_len;
+
+	return rht_bucket_index(tbl, params.hashfn(key, key_len,
 						   tbl->hash_rnd));
 }