linux-kernel - Re: [PATCH v4 12/13] blk-mq: Use shared tags for shared sbitmap support

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Date:   Mon, 27 Sep 2021 17:26:30 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        hare@...e.de
Subject: Re: [PATCH v4 12/13] blk-mq: Use shared tags for shared sbitmap
 support

On Mon, Sep 27, 2021 at 10:13:29AM +0100, John Garry wrote:
> On 26/09/2021 04:25, Ming Lei wrote:
> > > c
> > > @@ -27,10 +27,11 @@ bool __blk_mq_tag_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;
> > > +		struct blk_mq_tags *tags = set->shared_sbitmap_tags;
> > The local variable of 'set' can be removed and just retrieve 'tags' from
> > hctx->tags.
> > 
> > >   		if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) &&
> > >   		    !test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
> > > -			atomic_inc(&set->active_queues_shared_sbitmap);
> > > +			atomic_inc(&tags->active_queues);
> > >   	} else {
> > >   		if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
> > >   		    !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
> > > @@ -61,10 +62,12 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
> > >   	struct blk_mq_tag_set *set = q->tag_set;
> > >   	if (blk_mq_is_sbitmap_shared(hctx->flags)) {
> > > +		struct blk_mq_tags *tags = set->shared_sbitmap_tags;
> > > +
> > Same with above.
> 
> ok
> 
> > 
> > >   		if (!test_and_clear_bit(QUEUE_FLAG_HCTX_ACTIVE,
> > >   					&q->queue_flags))
> > >   			return;
> > > -		atomic_dec(&set->active_queues_shared_sbitmap);
> > > +		atomic_dec(&tags->active_queues);
> > >   	} else {
> > >   		if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
> > >   			return;
> > > @@ -510,38 +513,10 @@ static int blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
> > >   	return 0;
> > >   }
> 
> ...
> 
> > > -	struct sbitmap_queue	__bitmap_tags;
> > > -	struct sbitmap_queue	__breserved_tags;
> > >   	struct blk_mq_tags	**tags;
> > > +	struct blk_mq_tags	*shared_sbitmap_tags;
> > > +
> > >   	struct mutex		tag_list_lock;
> > >   	struct list_head	tag_list;
> > >   };
> > > @@ -432,6 +429,8 @@ enum {
> > >   	((policy & ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1)) \
> > >   		<< BLK_MQ_F_ALLOC_POLICY_START_BIT)
> > > +#define BLK_MQ_NO_HCTX_IDX	(-1U)
> > > +
> > >   struct gendisk *__blk_mq_alloc_disk(struct blk_mq_tag_set *set, void *queuedata,
> > >   		struct lock_class_key *lkclass);
> > >   #define blk_mq_alloc_disk(set, queuedata)				\
> > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> > > index 4baf9435232d..17e50e5ef47b 100644
> > > --- a/include/linux/blkdev.h
> > > +++ b/include/linux/blkdev.h
> > > @@ -459,8 +459,7 @@ struct request_queue {
> > >   	atomic_t		nr_active_requests_shared_sbitmap;
> > > -	struct sbitmap_queue	sched_bitmap_tags;
> > > -	struct sbitmap_queue	sched_breserved_tags;
> > > +	struct blk_mq_tags	*shared_sbitmap_tags;
> > Maybe better with shared_sched_sbitmap_tags or sched_sbitmap_tags?
> 
> Yeah, I suppose I should add "sched" to the name, as before.
> 
> BTW, Do you think that I should just change shared_sbitmap -> shared_tags
> naming now globally? I'm thinking now that I should...

Yeah, I think so, but seems you preferred to the name of shared sbitmap, so I
did't mention that, :-)


Thanks,
Ming