Re: [PATCH v6 1/4] block: Make fair tag sharing configurable

[Johannes Thumshirn <Johannes.Thumshirn@xxxxxxx>]

On 30.11.23 20:31, Bart Van Assche wrote:
> +void blk_mq_update_fair_sharing(struct blk_mq_tag_set *set, bool enable)
> +{
> +	const unsigned int DFTS_BIT = ilog2(BLK_MQ_F_DISABLE_FAIR_TAG_SHARING);
> +	struct blk_mq_hw_ctx *hctx;
> +	struct request_queue *q;
> +	unsigned long i;
> +
> +	/*
> +	 * Serialize against blk_mq_update_nr_hw_queues() and
> +	 * blk_mq_realloc_hw_ctxs().
> +	 */
> +	mutex_lock(&set->tag_list_lock);
> +	list_for_each_entry(q, &set->tag_list, tag_set_list)
> +		blk_mq_freeze_queue(q);
> +	assign_bit(DFTS_BIT, &set->flags, !enable);
> +	list_for_each_entry(q, &set->tag_list, tag_set_list)
> +		queue_for_each_hw_ctx(q, hctx, i)
> +			assign_bit(DFTS_BIT, &hctx->flags, !enable);
> +	list_for_each_entry(q, &set->tag_list, tag_set_list)
> +		blk_mq_unfreeze_queue(q);
> +	mutex_unlock(&set->tag_list_lock);

Hi Bart,

The above code adds a 3rd user (at least) of the following pattern to 
the kernel:

	list_for_each_entry(q, &set->tag_list, tag_set_list)
		blk_mq_freeze_queue(q);

	/* do stuff */

	list_for_each_entry(q, &set->tag_list, tag_set_list)
		blk_mq_unfreeze_queue(q);

Would it maybe be beneficial if we'd introduce functions for this, like:

static inline void blk_mq_freeze_tag_set(struct blk_mq_tag_set *set)
{
	lockdep_assert_held(&set->tag_list_lock);

	list_for_each_entry(q, &set->tag_list, tag_set_list)
		blk_mq_freeze_queue(q);
}

static inline void blk_mq_unfreeze_tag_set(struct blk_mq_tag_set *set)
{
	lockdep_assert_held(&set->tag_list_lock);

	list_for_each_entry(q, &set->tag_list, tag_set_list)
		blk_mq_unfreeze_queue(q);
}