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

[Mathieu Desnoyers]

* 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 ?

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
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com