netdev - [PATCH 1/2 net-next] rhashtable: Avoid calculating hash again to unlock

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Date:	Mon, 16 Mar 2015 10:42:26 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, herbert@...dor.apana.org.au
Subject: [PATCH 1/2 net-next] rhashtable: Avoid calculating hash again to unlock

Caching the lock pointer avoids having to hash on the object
again to unlock the bucket locks.

Signed-off-by: Thomas Graf <tgraf@...g.ch>
---
 lib/rhashtable.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index c523d3a..e396d7e 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -384,14 +384,16 @@ static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
 	struct rhash_head *head;
 	bool no_resize_running;
 	unsigned hash;
+	spinlock_t *old_lock;
 	bool success = true;
 
 	rcu_read_lock();
 
 	old_tbl = rht_dereference_rcu(ht->tbl, ht);
 	hash = head_hashfn(ht, old_tbl, obj);
+	old_lock = bucket_lock(old_tbl, hash);
 
-	spin_lock_bh(bucket_lock(old_tbl, hash));
+	spin_lock_bh(old_lock);
 
 	/* Because we have already taken the bucket lock in old_tbl,
 	 * if we find that future_tbl is not yet visible then that
@@ -428,13 +430,10 @@ static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
 		schedule_work(&ht->run_work);
 
 exit:
-	if (tbl != old_tbl) {
-		hash = head_hashfn(ht, tbl, obj);
+	if (tbl != old_tbl)
 		spin_unlock(bucket_lock(tbl, hash));
-	}
 
-	hash = head_hashfn(ht, old_tbl, obj);
-	spin_unlock_bh(bucket_lock(old_tbl, hash));
+	spin_unlock_bh(old_lock);
 
 	rcu_read_unlock();
 
-- 
1.9.3

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