Re: [PATCH] blk-mq: Use request queue-wide tags for tagset-wide sbitmap

[John Garry]

On 06/05/2021 09:32, Ming Lei wrote:
> > +	if (blk_mq_is_sbitmap_shared(q->tag_set->flags)) {
> > +		ret = blk_mq_init_sched_shared_sbitmap(q);
> > +		if (ret)
> > +			goto err_free_tags;
> > +
> > +		queue_for_each_hw_ctx(q, hctx, i) {
> > +			hctx->sched_tags->bitmap_tags =
> > +					q->sched_bitmap_tags;
> > +			hctx->sched_tags->breserved_tags =
> > +					q->sched_breserved_tags;
> > +		}
> >   	}
> >   
> >   	ret = e->ops.init_sched(q, e);
> >   	if (ret)
> > -		goto err;
> > +		goto err_free_sbitmap;
> >   
> >   	blk_mq_debugfs_register_sched(q);
> >   
> > @@ -584,6 +590,7 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
> >   				eq = q->elevator;
> >   				blk_mq_sched_free_requests(q);
> >   				blk_mq_exit_sched(q, eq);
> > +				blk_mq_exit_sched_shared_sbitmap(q);
> blk_mq_exit_sched_shared_sbitmap() has been called in blk_mq_exit_sched() already.

ah, yes

> >   				kobject_put(&eq->kobj);
> >   				return ret;
> >   			}
> > @@ -593,7 +600,10 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
> >   
> >   	return 0;
> >   
> > -err:
> > +err_free_sbitmap:
> > +	if (blk_mq_is_sbitmap_shared(q->tag_set->flags))
> > +		blk_mq_exit_sched_shared_sbitmap(q);
> > +err_free_tags:
> >   	blk_mq_sched_free_requests(q);
> >   	blk_mq_sched_tags_teardown(q);
> >   	q->elevator = NULL;
> > @@ -631,5 +641,7 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
> >   	if (e->type->ops.exit_sched)
> >   		e->type->ops.exit_sched(e);
> >   	blk_mq_sched_tags_teardown(q);
> > +	if (blk_mq_is_sbitmap_shared(q->tag_set->flags))
> > +		blk_mq_exit_sched_shared_sbitmap(q);
> >   	q->elevator = NULL;
> >   }
> > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> > index 2a37731e8244..734fedceca7d 100644
> > --- a/block/blk-mq-tag.c
> > +++ b/block/blk-mq-tag.c
> > @@ -466,19 +466,40 @@ static int blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
> >   	return -ENOMEM;
> >   }
> >   
> > -int blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *set, unsigned int flags)
> > +static int __blk_mq_init_bitmaps(struct sbitmap_queue *bitmap_tags,
> > +				 struct sbitmap_queue *breserved_tags,
> > +				 struct blk_mq_tag_set *set,
> > +				 unsigned int queue_depth,
> > +				 unsigned int reserved)
> >   {
> > -	unsigned int depth = set->queue_depth - set->reserved_tags;
> > +	unsigned int depth = queue_depth - reserved;
> >   	int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags);
> >   	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
> > -	int i, node = set->numa_node;
> >   
> > -	if (bt_alloc(&set->__bitmap_tags, depth, round_robin, node))
> > +	if (bt_alloc(bitmap_tags, depth, round_robin, set->numa_node))
> >   		return -ENOMEM;
> > -	if (bt_alloc(&set->__breserved_tags, set->reserved_tags,
> > -		     round_robin, node))
> > +	if (bt_alloc(breserved_tags, set->reserved_tags,
> > +		     round_robin, set->numa_node))
> >   		goto free_bitmap_tags;
> >   
> > +	return 0;
> > +
> > +free_bitmap_tags:
> > +	sbitmap_queue_free(bitmap_tags);
> > +	return -ENOMEM;
> > +}
> > +
> > +int blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *set)
> IMO, this function should be named as blk_mq_init_shared_tags
> and moved to blk-mq-sched.c

But this is for regular tags.

I assume you mean blk_mq_init_sched_shared_sbitmap(), below.

If so, I can relocate it.

As for "sbitmap" vs "tags" in the name, I'm just being consistent 
between preexisting blk_mq_init_shared_sbitmap() and 
blk_mq_sbitmap_shared(),  and new blk_mq_init_sched_shared_sbitmap()

> > +{
> > +	int i, ret;
> > +
> > +	ret = __blk_mq_init_bitmaps(&set->__bitmap_tags,
> > +				    &set->__breserved_tags,
> > +				    set, set->queue_depth,
> > +				    set->reserved_tags);
> > +	if (ret)
> > +		return ret;
> > +
> >   	for (i = 0; i < set->nr_hw_queues; i++) {
> >   		struct blk_mq_tags *tags = set->tags[i];
> >   
> > @@ -487,9 +508,6 @@ int blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *set, unsigned int flags)
> >   	}
> >   
> >   	return 0;
> > -free_bitmap_tags:
> > -	sbitmap_queue_free(&set->__bitmap_tags);
> > -	return -ENOMEM;
> >   }
> >   
> >   void blk_mq_exit_shared_sbitmap(struct blk_mq_tag_set *set)
> > @@ -498,6 +516,52 @@ void blk_mq_exit_shared_sbitmap(struct blk_mq_tag_set *set)
> >   	sbitmap_queue_free(&set->__breserved_tags);
> >   }
> >   
> > +#define MAX_SCHED_RQ (16 * BLKDEV_MAX_RQ)
> > +
> > +int blk_mq_init_sched_shared_sbitmap(struct request_queue *queue)
> > +{
> > +	struct blk_mq_tag_set *set = queue->tag_set;
> > +	int ret;
> > +
> > +	queue->sched_bitmap_tags =
> > +		kmalloc(sizeof(*queue->sched_bitmap_tags), GFP_KERNEL);
> > +	queue->sched_breserved_tags =
> > +		kmalloc(sizeof(*queue->sched_breserved_tags), GFP_KERNEL);
> > +	if (!queue->sched_bitmap_tags || !queue->sched_breserved_tags)
> > +		goto err;
> The two sbitmap queues can be embedded into 'request queue', so that
> we can avoid to re-allocation in every elevator switch.

ok

> I will ask Yanhui to test the patch and see if it can make a difference.

Thanks