[ltt-dev] [PATCH 4/9] rculfhash: merge dumplicated code for looking up bucket

[Lai Jiangshan]

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(-)
>>
>> diff --git a/rculfhash.c b/rculfhash.c
>> index 49f3637..1c859ed 100644
>> --- a/rculfhash.c
>> +++ b/rculfhash.c
>> @@ -711,6 +711,22 @@ 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.
>>   */
>> @@ -767,7 +783,6 @@ 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;
>> @@ -812,11 +827,7 @@ 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:
>> @@ -841,7 +852,6 @@ 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));
>> @@ -850,7 +860,7 @@ 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;
>>  
>> @@ -858,9 +868,6 @@ 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)];
> 
> 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.

> 
> Thanks,
> 
> Mathieu
> 
>>  		iter_prev = (struct cds_lfht_node *) lookup;
>>  		/* We can always skip the dummy node initially */
>>  		iter = rcu_dereference(iter_prev->p.next);
>> @@ -936,9 +943,6 @@ 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:
>> @@ -953,7 +957,6 @@ 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;
>> @@ -984,11 +987,7 @@ 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:
>> @@ -1313,17 +1312,13 @@ 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);
>> -- 
>> 1.7.4.4
>>
>