Re: [PATCH 2/9] sbitmap: add helper to clear a batch of tags

[Bart Van Assche <bvanassche@xxxxxxx>]

On 10/12/21 11:17 AM, Jens Axboe wrote:
> +void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset,
> +				int *tags, int nr_tags)
> +{
> +	struct sbitmap *sb = &sbq->sb;
> +	unsigned long *addr = NULL;
> +	unsigned long mask = 0;
> +	int i;
> +
> +	smp_mb__before_atomic();
> +	for (i = 0; i < nr_tags; i++) {
> +		const int tag = tags[i] - offset;
> +		unsigned long *this_addr;
> +
> +		/* since we're clearing a batch, skip the deferred map */
> +		this_addr = &sb->map[SB_NR_TO_INDEX(sb, tag)].word;
> +		if (!addr) {
> +			addr = this_addr;
> +		} else if (addr != this_addr) {
> +			atomic_long_andnot(mask, (atomic_long_t *) addr);
> +			mask = 0;
> +			addr = this_addr;
> +		}
> +		mask |= (1UL << SB_NR_TO_BIT(sb, tag));
> +	}
> +
> +	if (mask)
> +		atomic_long_andnot(mask, (atomic_long_t *) addr);
> +
> +	smp_mb__after_atomic();
> +	sbitmap_queue_wake_up(sbq);
> +	sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
> +					tags[nr_tags - 1] - offset);
> +}
> +
>   void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
>   			 unsigned int cpu)
>   {

How does replacing the sbitmap_queue_clear() implementation by calling 
sbitmap_queue_clear_batch() affect performance? I'm wondering whether it 
is possible to prevent code duplication without affecting performance 
negatively.

Thanks,

Bart.