diff mbox

[net-next,v2,5/7] rhashtable: avoid unnecessary wakeup for worker queue

Message ID 1420609318-3261-6-git-send-email-ying.xue@windriver.com
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Ying Xue Jan. 7, 2015, 5:41 a.m. UTC 
Move condition statements of verifying whether hash table size exceeds
its maximum threshold or reaches its minimum threshold from resizing
functions to resizing decision functions, avoiding unnecessary wakeup
for worker queue thread.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Thomas Graf <tgraf@suug.ch>
---
 include/linux/rhashtable.h |    2 +-
 lib/rhashtable.c           |   18 +++++++-----------
 2 files changed, 8 insertions(+), 12 deletions(-)

Comments

Thomas Graf Jan. 7, 2015, 9:50 a.m. UTC | #1 
On 01/07/15 at 01:41pm, Ying Xue wrote:
> Move condition statements of verifying whether hash table size exceeds
> its maximum threshold or reaches its minimum threshold from resizing
> functions to resizing decision functions, avoiding unnecessary wakeup
> for worker queue thread.
> 
> Signed-off-by: Ying Xue <ying.xue@windriver.com>
> Cc: Thomas Graf <tgraf@suug.ch>

Good optimization, thanks!

Acked-by: Thomas Graf <tgraf@suug.ch>

Can you do a follow-up patch and add a note in rhashtable.h to
indicate the implementation of the grow and shrink decision function
must enforce min/max shift?
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Ying Xue Jan. 7, 2015, 10:28 a.m. UTC | #2 
On 01/07/2015 05:50 PM, Thomas Graf wrote:
> On 01/07/15 at 01:41pm, Ying Xue wrote:
>> Move condition statements of verifying whether hash table size exceeds
>> its maximum threshold or reaches its minimum threshold from resizing
>> functions to resizing decision functions, avoiding unnecessary wakeup
>> for worker queue thread.
>>
>> Signed-off-by: Ying Xue <ying.xue@windriver.com>
>> Cc: Thomas Graf <tgraf@suug.ch>
> 
> Good optimization, thanks!
> 
> Acked-by: Thomas Graf <tgraf@suug.ch>
> 
> Can you do a follow-up patch and add a note in rhashtable.h to
> indicate the implementation of the grow and shrink decision function
> must enforce min/max shift?
> 
> 

Thanks for the reminder, and I will do this later.

Regards,
Ying

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diff mbox

Patch

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 73c913f..326acd8 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -113,7 +113,7 @@  struct rhashtable {
 	struct bucket_table __rcu	*tbl;
 	struct bucket_table __rcu       *future_tbl;
 	atomic_t			nelems;
-	size_t				shift;
+	atomic_t			shift;
 	struct rhashtable_params	p;
 	struct delayed_work             run_work;
 	struct mutex                    mutex;
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 1aef942..7fb474b 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -199,7 +199,8 @@  static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size)
 {
 	/* Expand table when exceeding 75% load */
-	return atomic_read(&ht->nelems) > (new_size / 4 * 3);
+	return atomic_read(&ht->nelems) > (new_size / 4 * 3) &&
+	       (ht->p.max_shift && atomic_read(&ht->shift) < ht->p.max_shift);
 }
 EXPORT_SYMBOL_GPL(rht_grow_above_75);
 
@@ -211,7 +212,8 @@  EXPORT_SYMBOL_GPL(rht_grow_above_75);
 bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size)
 {
 	/* Shrink table beneath 30% load */
-	return atomic_read(&ht->nelems) < (new_size * 3 / 10);
+	return atomic_read(&ht->nelems) < (new_size * 3 / 10) &&
+	       (atomic_read(&ht->shift) > ht->p.min_shift);
 }
 EXPORT_SYMBOL_GPL(rht_shrink_below_30);
 
@@ -318,14 +320,11 @@  int rhashtable_expand(struct rhashtable *ht)
 
 	ASSERT_RHT_MUTEX(ht);
 
-	if (ht->p.max_shift && ht->shift >= ht->p.max_shift)
-		return 0;
-
 	new_tbl = bucket_table_alloc(ht, old_tbl->size * 2);
 	if (new_tbl == NULL)
 		return -ENOMEM;
 
-	ht->shift++;
+	atomic_inc(&ht->shift);
 
 	/* Make insertions go into the new, empty table right away. Deletions
 	 * and lookups will be attempted in both tables until we synchronize.
@@ -421,9 +420,6 @@  int rhashtable_shrink(struct rhashtable *ht)
 
 	ASSERT_RHT_MUTEX(ht);
 
-	if (ht->shift <= ht->p.min_shift)
-		return 0;
-
 	new_tbl = bucket_table_alloc(ht, tbl->size / 2);
 	if (new_tbl == NULL)
 		return -ENOMEM;
@@ -462,7 +458,7 @@  int rhashtable_shrink(struct rhashtable *ht)
 
 	/* Publish the new, valid hash table */
 	rcu_assign_pointer(ht->tbl, new_tbl);
-	ht->shift--;
+	atomic_dec(&ht->shift);
 
 	/* Wait for readers. No new readers will have references to the
 	 * old hash table.
@@ -851,7 +847,7 @@  int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
 	if (tbl == NULL)
 		return -ENOMEM;
 
-	ht->shift = ilog2(tbl->size);
+	atomic_set(&ht->shift, ilog2(tbl->size));
 	RCU_INIT_POINTER(ht->tbl, tbl);
 	RCU_INIT_POINTER(ht->future_tbl, tbl);