[ltt-dev] [PATCH 4/9] rculfhash: merge dumplicated code for looking up bucket
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Mon Oct 17 09:44:16 EDT 2011
* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> On 10/14/2011 10:12 PM, Mathieu Desnoyers wrote:
> > * Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> >> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> >> ---
> >> rculfhash.c | 47 +++++++++++++++++++++--------------------------
> >> 1 files changed, 21 insertions(+), 26 deletions(-)
> >>
[...]
> >
> > There is a reason why the lookup bucket is done in the loop and in the
> > gc_end path below: it deals with concurrent hash table resizes. So I
> > agree that merging these code paths into lookup_bucket is good, but I
> > think you are changing the behavior here.
> >
> > Or maybe you have something else in mind that guarantees that the change
> > you do here is correct ?
>
> hash and size are constant here,
> so the lookup can be moved up.
>
Merged as:
commit f4a9cc0b4bc9791e18c66b00023ae4ef76befb74
Author: Lai Jiangshan <laijs at cn.fujitsu.com>
Date: Mon Oct 17 09:46:10 2011 -0400
rculfhash: merge duplicated code for bucket lookup
[ Edit by Mathieu Desnoyers: also remove unnecessary lookups that end up
returning an already looked up node. Same behavior is guaranteed
because the hash and size stay invariant across retry. ]
Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
diff --git a/rculfhash.c b/rculfhash.c
index 2e338f1..c7b9ea8 100644
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -716,6 +716,22 @@ unsigned long _uatomic_max(unsigned long *ptr, unsigned long v)
return v;
}
+static
+struct _cds_lfht_node *lookup_bucket(struct cds_lfht *ht, unsigned long size,
+ unsigned long hash)
+{
+ unsigned long index, order;
+
+ assert(size > 0);
+ index = hash & (size - 1);
+ order = get_count_order_ulong(index + 1);
+
+ dbg_printf("lookup hash %lu index %lu order %lu aridx %lu\n",
+ hash, index, order, index & (!order ? 0 : ((1UL << (order - 1)) - 1)));
+
+ return &ht->t.tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1)) - 1))];
+}
+
/*
* Remove all logically deleted nodes from a bucket up to a certain node key.
*/
@@ -772,7 +788,6 @@ int _cds_lfht_replace(struct cds_lfht *ht, unsigned long size,
struct cds_lfht_node *dummy, *old_next;
struct _cds_lfht_node *lookup;
int flagged = 0;
- unsigned long hash, index, order;
if (!old_node) /* Return -ENOENT if asked to replace NULL node */
goto end;
@@ -817,11 +832,7 @@ int _cds_lfht_replace(struct cds_lfht *ht, unsigned long size,
* lookup for the node, and remove it (along with any other
* logically removed node) if found.
*/
- hash = bit_reverse_ulong(old_node->p.reverse_hash);
- assert(size > 0);
- index = hash & (size - 1);
- order = get_count_order_ulong(index + 1);
- lookup = &ht->t.tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1)) - 1))];
+ lookup = lookup_bucket(ht, size, bit_reverse_ulong(old_node->p.reverse_hash));
dummy = (struct cds_lfht_node *) lookup;
_cds_lfht_gc_bucket(dummy, new_node);
end:
@@ -846,7 +857,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
struct cds_lfht_node *iter_prev, *iter, *next, *new_node, *new_next,
*dummy_node, *return_node;
struct _cds_lfht_node *lookup;
- unsigned long hash, index, order;
assert(!is_dummy(node));
assert(!is_removed(node));
@@ -855,7 +865,7 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
node->p.next = flag_dummy(get_end());
return node; /* Initial first add (head) */
}
- hash = bit_reverse_ulong(node->p.reverse_hash);
+ lookup = lookup_bucket(ht, size, bit_reverse_ulong(node->p.reverse_hash));
for (;;) {
uint32_t chain_len = 0;
@@ -863,9 +873,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
* iter_prev points to the non-removed node prior to the
* insert location.
*/
- index = hash & (size - 1);
- order = get_count_order_ulong(index + 1);
- lookup = &ht->t.tbl[order]->nodes[index & ((!order ? 0 : (1UL << (order - 1))) - 1)];
iter_prev = (struct cds_lfht_node *) lookup;
/* We can always skip the dummy node initially */
iter = rcu_dereference(iter_prev->p.next);
@@ -941,9 +948,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
}
gc_end:
/* Garbage collect logically removed nodes in the bucket */
- index = hash & (size - 1);
- order = get_count_order_ulong(index + 1);
- lookup = &ht->t.tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1)) - 1))];
dummy_node = (struct cds_lfht_node *) lookup;
_cds_lfht_gc_bucket(dummy_node, node);
end:
@@ -958,7 +962,6 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
struct cds_lfht_node *dummy, *next, *old;
struct _cds_lfht_node *lookup;
int flagged = 0;
- unsigned long hash, index, order;
if (!node) /* Return -ENOENT if asked to delete NULL node */
goto end;
@@ -989,11 +992,7 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
* the node, and remove it (along with any other logically removed node)
* if found.
*/
- hash = bit_reverse_ulong(node->p.reverse_hash);
- assert(size > 0);
- index = hash & (size - 1);
- order = get_count_order_ulong(index + 1);
- lookup = &ht->t.tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1)) - 1))];
+ lookup = lookup_bucket(ht, size, bit_reverse_ulong(node->p.reverse_hash));
dummy = (struct cds_lfht_node *) lookup;
_cds_lfht_gc_bucket(dummy, node);
end:
@@ -1318,17 +1317,13 @@ void cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len,
{
struct cds_lfht_node *node, *next, *dummy_node;
struct _cds_lfht_node *lookup;
- unsigned long hash, reverse_hash, index, order, size;
+ unsigned long hash, reverse_hash, size;
hash = ht->hash_fct(key, key_len, ht->hash_seed);
reverse_hash = bit_reverse_ulong(hash);
size = rcu_dereference(ht->t.size);
- index = hash & (size - 1);
- order = get_count_order_ulong(index + 1);
- lookup = &ht->t.tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1))) - 1)];
- dbg_printf("lookup hash %lu index %lu order %lu aridx %lu\n",
- hash, index, order, index & (!order ? 0 : ((1UL << (order - 1)) - 1)));
+ lookup = lookup_bucket(ht, size, hash);
dummy_node = (struct cds_lfht_node *) lookup;
/* We can always skip the dummy node initially */
node = rcu_dereference(dummy_node->p.next);
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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