[ltt-dev] [PATCH 2/5] rculfhash: use hash for index if !HAVE_SCHED_GETCPU

[Mathieu Desnoyers]

Brilliant way to do split-counters based on the existing hashes :)

Merged, thanks !

Mathieu

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> ---
>  rculfhash.c |   50 ++++++++++++++++++++++++++++----------------------
>  1 files changed, 28 insertions(+), 22 deletions(-)
> 
> diff --git a/rculfhash.c b/rculfhash.c
> index d1bec03..ea6df05 100644
> --- a/rculfhash.c
> +++ b/rculfhash.c
> @@ -506,7 +506,7 @@ void cds_lfht_resize_lazy(struct cds_lfht *ht, unsigned long size, int growth);
>   * In the unfortunate event the number of CPUs reported would be
>   * inaccurate, we use modulo arithmetic on the number of CPUs we got.
>   */
> -#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
> +#if defined(HAVE_SYSCONF)
>  
>  static
>  void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
> @@ -554,30 +554,36 @@ void free_split_items_count(struct ht_items_count *count)
>  	poison_free(count);
>  }
>  
> +#if defined(HAVE_SCHED_GETCPU)
>  static
> -int ht_get_split_count_index(void)
> +int ht_get_split_count_index(unsigned long hash)
>  {
>  	int cpu;
>  
>  	assert(split_count_mask >= 0);
>  	cpu = sched_getcpu();
>  	if (unlikely(cpu < 0))
> -		return cpu;
> +		return hash & split_count_mask;
>  	else
>  		return cpu & split_count_mask;
>  }
> +#else /* #if defined(HAVE_SCHED_GETCPU) */
> +static
> +int ht_get_split_count_index(unsigned long hash)
> +{
> +	return hash & split_count_mask;
> +}
> +#endif /* #else #if defined(HAVE_SCHED_GETCPU) */
>  
>  static
> -void ht_count_add(struct cds_lfht *ht, unsigned long size)
> +void ht_count_add(struct cds_lfht *ht, unsigned long size, unsigned long hash)
>  {
>  	unsigned long split_count;
>  	int index;
>  
>  	if (unlikely(!ht->split_count))
>  		return;
> -	index = ht_get_split_count_index();
> -	if (unlikely(index < 0))
> -		return;
> +	index = ht_get_split_count_index(hash);
>  	split_count = uatomic_add_return(&ht->split_count[index].add, 1);
>  	if (unlikely(!(split_count & ((1UL << COUNT_COMMIT_ORDER) - 1)))) {
>  		long count;
> @@ -597,16 +603,14 @@ void ht_count_add(struct cds_lfht *ht, unsigned long size)
>  }
>  
>  static
> -void ht_count_del(struct cds_lfht *ht, unsigned long size)
> +void ht_count_del(struct cds_lfht *ht, unsigned long size, unsigned long hash)
>  {
>  	unsigned long split_count;
>  	int index;
>  
>  	if (unlikely(!ht->split_count))
>  		return;
> -	index = ht_get_split_count_index();
> -	if (unlikely(index < 0))
> -		return;
> +	index = ht_get_split_count_index(hash);
>  	split_count = uatomic_add_return(&ht->split_count[index].del, 1);
>  	if (unlikely(!(split_count & ((1UL << COUNT_COMMIT_ORDER) - 1)))) {
>  		long count;
> @@ -631,7 +635,7 @@ void ht_count_del(struct cds_lfht *ht, unsigned long size)
>  	}
>  }
>  
> -#else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
> +#else /* #if defined(HAVE_SYSCONF) */
>  
>  static const long nr_cpus_mask = -2;
>  static const long split_count_mask = -2;
> @@ -648,16 +652,16 @@ void free_split_items_count(struct ht_items_count *count)
>  }
>  
>  static
> -void ht_count_add(struct cds_lfht *ht, unsigned long size)
> +void ht_count_add(struct cds_lfht *ht, unsigned long size, unsigned long hash)
>  {
>  }
>  
>  static
> -void ht_count_del(struct cds_lfht *ht, unsigned long size)
> +void ht_count_del(struct cds_lfht *ht, unsigned long size, unsigned long hash)
>  {
>  }
>  
> -#endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
> +#endif /* #else #if defined(HAVE_SYSCONF) */
>  
>  
>  static
> @@ -1504,7 +1508,7 @@ void cds_lfht_add(struct cds_lfht *ht, struct cds_lfht_node *node)
>  
>  	size = rcu_dereference(ht->t.size);
>  	_cds_lfht_add(ht, size, node, NULL, 0);
> -	ht_count_add(ht, size);
> +	ht_count_add(ht, size, hash);
>  }
>  
>  struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht,
> @@ -1519,7 +1523,7 @@ struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht,
>  	size = rcu_dereference(ht->t.size);
>  	_cds_lfht_add(ht, size, node, &iter, 0);
>  	if (iter.node == node)
> -		ht_count_add(ht, size);
> +		ht_count_add(ht, size, hash);
>  	return iter.node;
>  }
>  
> @@ -1536,7 +1540,7 @@ struct cds_lfht_node *cds_lfht_add_replace(struct cds_lfht *ht,
>  	for (;;) {
>  		_cds_lfht_add(ht, size, node, &iter, 0);
>  		if (iter.node == node) {
> -			ht_count_add(ht, size);
> +			ht_count_add(ht, size, hash);
>  			return NULL;
>  		}
>  
> @@ -1557,13 +1561,15 @@ int cds_lfht_replace(struct cds_lfht *ht, struct cds_lfht_iter *old_iter,
>  
>  int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_iter *iter)
>  {
> -	unsigned long size;
> +	unsigned long size, hash;
>  	int ret;
>  
>  	size = rcu_dereference(ht->t.size);
>  	ret = _cds_lfht_del(ht, size, iter->node, 0);
> -	if (!ret)
> -		ht_count_del(ht, size);
> +	if (!ret) {
> +		hash = bit_reverse_ulong(iter->node->p.reverse_hash);
> +		ht_count_del(ht, size, hash);
> +	}
>  	return ret;
>  }
>  
> @@ -1809,7 +1815,7 @@ void cds_lfht_resize_lazy(struct cds_lfht *ht, unsigned long size, int growth)
>  	}
>  }
>  
> -#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
> +#if defined(HAVE_SYSCONF)
>  
>  static
>  void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
> -- 
> 1.7.4.4
> 

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