Re: [PATCH] blk-mq: allow hardware queue to get more tag while sharing a tag set

["yukuai (C)" <yukuai3@huawei.com>]

On 2021/07/12 11:18, Yu Kuai wrote:
> If there are multiple active queues while sharing a tag set, it's not
> necessary to limit the available tags as same share for each active queue
> if no one ever failed to get driver tag. And fall back to same share if
> someone do failed to get driver tag.
> 
> This modification will be beneficial if total queue_depth of disks
> on the same host is less than total tags.

Sorry this should be "more than", I'll correct this in next iteration
if anyone think this patch is acceptable.

Thanks,
Yu Kuai
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>   block/blk-mq-debugfs.c |  2 ++
>   block/blk-mq-tag.c     | 43 +++++++++++++++++++++++++++++++++++++++++-
>   block/blk-mq-tag.h     | 27 ++++++++++++++++++++++++--
>   block/blk-mq.c         | 13 ++++++++++---
>   block/blk-mq.h         |  8 ++++++++
>   include/linux/blk-mq.h |  4 ++++
>   include/linux/blkdev.h |  1 +
>   7 files changed, 92 insertions(+), 6 deletions(-)
> 
> diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
> index 4b66d2776eda..35f1f01d93ae 100644
> --- a/block/blk-mq-debugfs.c
> +++ b/block/blk-mq-debugfs.c
> @@ -450,6 +450,8 @@ static void blk_mq_debugfs_tags_show(struct seq_file *m,
>   	seq_printf(m, "nr_reserved_tags=%u\n", tags->nr_reserved_tags);
>   	seq_printf(m, "active_queues=%d\n",
>   		   atomic_read(&tags->active_queues));
> +	seq_printf(m, "pending_queues=%d\n",
> +		   atomic_read(&tags->pending_queues));
>   
>   	seq_puts(m, "\nbitmap_tags:\n");
>   	sbitmap_queue_show(tags->bitmap_tags, m);
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 86f87346232a..618624b359d6 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -40,6 +40,22 @@ bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
>   	return true;
>   }
>   
> +void __blk_mq_dtag_busy(struct blk_mq_hw_ctx *hctx)
> +{
> +	if (blk_mq_is_sbitmap_shared(hctx->flags)) {
> +		struct request_queue *q = hctx->queue;
> +		struct blk_mq_tag_set *set = q->tag_set;
> +
> +		if (!test_bit(QUEUE_FLAG_HCTX_WAIT, &q->queue_flags) &&
> +		    !test_and_set_bit(QUEUE_FLAG_HCTX_WAIT, &q->queue_flags))
> +			atomic_inc(&set->pending_queues_shared_sbitmap);
> +	} else {
> +		if (!test_bit(BLK_MQ_S_DTAG_WAIT, &hctx->state) &&
> +		    !test_and_set_bit(BLK_MQ_S_DTAG_WAIT, &hctx->state))
> +			atomic_inc(&hctx->tags->pending_queues);
> +	}
> +}
> +
>   /*
>    * Wakeup all potentially sleeping on tags
>    */
> @@ -74,6 +90,24 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
>   	blk_mq_tag_wakeup_all(tags, false);
>   }
>   
> +void __blk_mq_dtag_idle(struct blk_mq_hw_ctx *hctx)
> +{
> +	struct blk_mq_tags *tags = hctx->tags;
> +	struct request_queue *q = hctx->queue;
> +	struct blk_mq_tag_set *set = q->tag_set;
> +
> +	if (blk_mq_is_sbitmap_shared(hctx->flags)) {
> +		if (!test_and_clear_bit(QUEUE_FLAG_HCTX_WAIT,
> +					&q->queue_flags))
> +			return;
> +		atomic_dec(&set->pending_queues_shared_sbitmap);
> +	} else {
> +		if (!test_and_clear_bit(BLK_MQ_S_DTAG_WAIT, &hctx->state))
> +			return;
> +		atomic_dec(&tags->pending_queues);
> +	}
> +}
> +
>   static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
>   			    struct sbitmap_queue *bt)
>   {
> @@ -112,8 +146,12 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
>   	if (tag != BLK_MQ_NO_TAG)
>   		goto found_tag;
>   
> -	if (data->flags & BLK_MQ_REQ_NOWAIT)
> +	if (data->flags & BLK_MQ_REQ_NOWAIT) {
> +		if (!data->q->elevator)
> +			blk_mq_dtag_busy(data->hctx);
> +
>   		return BLK_MQ_NO_TAG;
> +	}
>   
>   	ws = bt_wait_ptr(bt, data->hctx);
>   	do {
> @@ -140,6 +178,9 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
>   		if (tag != BLK_MQ_NO_TAG)
>   			break;
>   
> +		if (!data->q->elevator)
> +			blk_mq_dtag_busy(data->hctx);
> +
>   		bt_prev = bt;
>   		io_schedule();
>   
> diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
> index 8ed55af08427..badcf3693749 100644
> --- a/block/blk-mq-tag.h
> +++ b/block/blk-mq-tag.h
> @@ -10,6 +10,11 @@ struct blk_mq_tags {
>   	unsigned int nr_reserved_tags;
>   
>   	atomic_t active_queues;
> +	/*
> +	 * if multiple queues share a tag set, pending_queues record the
> +	 * number of queues that can't get driver tag.
> +	 */
> +	atomic_t pending_queues;
>   
>   	struct sbitmap_queue *bitmap_tags;
>   	struct sbitmap_queue *breserved_tags;
> @@ -69,8 +74,10 @@ enum {
>   	BLK_MQ_TAG_MAX		= BLK_MQ_NO_TAG - 1,
>   };
>   
> -extern bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *);
> -extern void __blk_mq_tag_idle(struct blk_mq_hw_ctx *);
> +extern bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx);
> +extern void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx);
> +extern void __blk_mq_dtag_busy(struct blk_mq_hw_ctx *hctx);
> +extern void __blk_mq_dtag_idle(struct blk_mq_hw_ctx *hctx);
>   
>   static inline bool blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
>   {
> @@ -88,6 +95,22 @@ static inline void blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
>   	__blk_mq_tag_idle(hctx);
>   }
>   
> +static inline void blk_mq_dtag_busy(struct blk_mq_hw_ctx *hctx)
> +{
> +	if (!(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED))
> +		return;
> +
> +	__blk_mq_dtag_busy(hctx);
> +}
> +
> +static inline void blk_mq_dtag_idle(struct blk_mq_hw_ctx *hctx)
> +{
> +	if (!(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED))
> +		return;
> +
> +	__blk_mq_dtag_idle(hctx);
> +}
> +
>   static inline bool blk_mq_tag_is_reserved(struct blk_mq_tags *tags,
>   					  unsigned int tag)
>   {
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2c4ac51e54eb..1bb52bd71da8 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -991,8 +991,10 @@ static void blk_mq_timeout_work(struct work_struct *work)
>   		 */
>   		queue_for_each_hw_ctx(q, hctx, i) {
>   			/* the hctx may be unmapped, so check it here */
> -			if (blk_mq_hw_queue_mapped(hctx))
> +			if (blk_mq_hw_queue_mapped(hctx)) {
>   				blk_mq_tag_idle(hctx);
> +				blk_mq_dtag_idle(hctx);
> +			}
>   		}
>   	}
>   	blk_queue_exit(q);
> @@ -1097,8 +1099,10 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
>   	}
>   
>   	tag = __sbitmap_queue_get(bt);
> -	if (tag == BLK_MQ_NO_TAG)
> +	if (tag == BLK_MQ_NO_TAG) {
> +		blk_mq_dtag_busy(rq->mq_hctx);
>   		return false;
> +	}
>   
>   	rq->tag = tag + tag_offset;
>   	return true;
> @@ -2676,8 +2680,10 @@ static void blk_mq_exit_hctx(struct request_queue *q,
>   {
>   	struct request *flush_rq = hctx->fq->flush_rq;
>   
> -	if (blk_mq_hw_queue_mapped(hctx))
> +	if (blk_mq_hw_queue_mapped(hctx)) {
>   		blk_mq_tag_idle(hctx);
> +		blk_mq_dtag_idle(hctx);
> +	}
>   
>   	blk_mq_clear_flush_rq_mapping(set->tags[hctx_idx],
>   			set->queue_depth, flush_rq);
> @@ -3536,6 +3542,7 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
>   
>   	if (blk_mq_is_sbitmap_shared(set->flags)) {
>   		atomic_set(&set->active_queues_shared_sbitmap, 0);
> +		atomic_set(&set->pending_queues_shared_sbitmap, 0);
>   
>   		if (blk_mq_init_shared_sbitmap(set)) {
>   			ret = -ENOMEM;
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index d08779f77a26..9e646ade81a8 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -337,10 +337,18 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
>   
>   		if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
>   			return true;
> +
> +		if (!atomic_read(&set->pending_queues_shared_sbitmap))
> +			return true;
> +
>   		users = atomic_read(&set->active_queues_shared_sbitmap);
>   	} else {
>   		if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
>   			return true;
> +
> +		if (!atomic_read(&hctx->tags->pending_queues))
> +			return true;
> +
>   		users = atomic_read(&hctx->tags->active_queues);
>   	}
>   
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 1d18447ebebc..3bc0faf0e2cf 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -256,6 +256,7 @@ struct blk_mq_tag_set {
>   	unsigned int		flags;
>   	void			*driver_data;
>   	atomic_t		active_queues_shared_sbitmap;
> +	atomic_t		pending_queues_shared_sbitmap;
>   
>   	struct sbitmap_queue	__bitmap_tags;
>   	struct sbitmap_queue	__breserved_tags;
> @@ -415,6 +416,9 @@ enum {
>   	/* hw queue is inactive after all its CPUs become offline */
>   	BLK_MQ_S_INACTIVE	= 3,
>   
> +	/* hw queue is waiting for driver tag */
> +	BLK_MQ_S_DTAG_WAIT	= 1,
> +
>   	BLK_MQ_MAX_DEPTH	= 10240,
>   
>   	BLK_MQ_CPU_WORK_BATCH	= 8,
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 3177181c4326..55e0965c9c3c 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -603,6 +603,7 @@ struct request_queue {
>   #define QUEUE_FLAG_RQ_ALLOC_TIME 27	/* record rq->alloc_time_ns */
>   #define QUEUE_FLAG_HCTX_ACTIVE	28	/* at least one blk-mq hctx is active */
>   #define QUEUE_FLAG_NOWAIT       29	/* device supports NOWAIT */
> +#define QUEUE_FLAG_HCTX_WAIT	30	/* at least one blk-mq hctx can't get driver tag */
>   
>   #define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
>   				 (1 << QUEUE_FLAG_SAME_COMP) |		\
>