Minor rhashtable fixes

PATCH Applied Thomas Graf 3 participants 7 messages Mar 16, 2015

Subsystems (4)

Networking Network drivers Library code Rhashtable

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Thomas Graf

author maintainer

2015-03-16 09:42 UTC #1 lore raw

PATCH v2 1/2 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 <[email protected]>

---
 lib/rhashtable.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

lib/rhashtable.c +5 -6

index c523d3a..e396d7e 100644
@@ -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();

Signature · 1 line

1.9.3

David Miller

maintainer

2015-03-16 20:22 UTC #2 lore raw

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

From: Thomas Graf <[email protected]>
Date: Mon, 16 Mar 2015 10:42:26 +0100

Quoted 4 lines

Caching the lock pointer avoids having to hash on the object again to unlock the bucket locks.
Signed-off-by Thomas Graf <[email protected]>

I'd like to hold off on this.

My understanding is that Herbert plans to expand the table size synchonously during insert in emergency situations, and in that regime some of these optimization won't be valid.

Herbert Xu

maintainer

2015-03-16 20:48 UTC #3 lore raw

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

Quoted 6 lines · David Miller

From: Thomas Graf <[email protected]>
Date: Mon, 16 Mar 2015 10:42:26 +0100
Quoted 3 lines
Caching the lock pointer avoids having to hash on the object again to unlock the bucket locks.

Quoted 7 lines

Quoted 1 line
Signed-off-by Thomas Graf <[email protected]>
I'd like to hold off on this.
My understanding is that Herbert plans to expand the table size synchonously during insert in emergency situations, and in that regime some of these optimization won't be valid.

Actually this patch does not conflict with my multiple rehashing work (the final scheme I used only requires two locks) so please feel free to merge it and I will rebase my stuff.

Thanks,

Signature · 3 lines

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

David Miller

maintainer

2015-03-16 21:15 UTC #4 lore raw

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

From: Herbert Xu <[email protected]>
Date: Tue, 17 Mar 2015 07:48:36 +1100

Quoted 11 lines · David Miller

Quoted 10 lines
From: Thomas Graf <[email protected]>
Date: Mon, 16 Mar 2015 10:42:26 +0100
Quoted 4 lines
Caching the lock pointer avoids having to hash on the object again to unlock the bucket locks.
Signed-off-by Thomas Graf <[email protected]>
I'd like to hold off on this.

Quoted 7 lines

Quoted 3 lines
My understanding is that Herbert plans to expand the table size synchonously during insert in emergency situations, and in that regime some of these optimization won't be valid.
Actually this patch does not conflict with my multiple rehashing work (the final scheme I used only requires two locks) so please feel free to merge it and I will rebase my stuff.

Ok, done, thanks.

Thomas Graf

author maintainer

2015-03-16 09:42 UTC #5 lore raw

PATCH v2 2/2 rhashtable: Annotate RCU locking of walkers

In reply to Thomas Graf

Fixes the following sparse warnings:

lib/rhashtable.c:767:5: warning: context imbalance in 'rhashtable_walk_start' - wrong count at exit lib/rhashtable.c:849:6: warning: context imbalance in 'rhashtable_walk_stop' - unexpected unlock

Fixes f2dba9c6ff0d ("rhashtable: Introduce rhashtable_walk_*")

Signed-off-by Thomas Graf <[email protected]>

---
 lib/rhashtable.c | 2 ++
 1 file changed, 2 insertions(+)

lib/rhashtable.c +2 -0

index e396d7e..09a7ada 100644
@@ -759,6 +759,7 @@ EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
  * by calling rhashtable_walk_next.
  */
 int rhashtable_walk_start(struct rhashtable_iter *iter)
+	__acquires(RCU)
 {
 	struct rhashtable *ht = iter->ht;

@@ -846,6 +847,7 @@ EXPORT_SYMBOL_GPL(rhashtable_walk_next);
  * Finish a hash table walk.
  */
 void rhashtable_walk_stop(struct rhashtable_iter *iter)
+	__releases(RCU)
 {
 	struct rhashtable *ht;
 	struct bucket_table *tbl = iter->walker->tbl;

Signature · 1 line

1.9.3

David Miller

maintainer Applied

2015-03-16 20:24 UTC #6 lore raw

Re: [PATCH 2/2 net-next] rhashtable: Annotate RCU locking of walkers

From: Thomas Graf <[email protected]>
Date: Mon, 16 Mar 2015 10:42:27 +0100

Quoted 7 lines

Fixes the following sparse warnings:
lib/rhashtable.c:767:5: warning: context imbalance in 'rhashtable_walk_start' - wrong count at exit lib/rhashtable.c:849:6: warning: context imbalance in 'rhashtable_walk_stop' - unexpected unlock
Fixes f2dba9c6ff0d ("rhashtable: Introduce rhashtable_walk_*")
Signed-off-by Thomas Graf <[email protected]>

Applied, thanks.