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

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

On 2021/07/20 20:33, yukuai (C) wrote:
> 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.
>>
>> 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) |        \
>>
> 
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