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Date: Fri, 23 Oct 2015 17:48:53 +0800 From: jason <zhangqing.luo@...cle.com> To: Jeff Moyer <jmoyer@...hat.com>, Jens Axboe <axboe@...nel.dk> CC: Tejun Heo <tj@...nel.org>, Guru Anbalagane <guru.anbalagane@...cle.com>, Feng Jin <joe.jin@...cle.com>, linux-kernel@...r.kernel.org Subject: Re: blk-mq: takes hours for scsi scanning finish when thousands of LUNs Hi,Jeff On Friday, October 23, 2015 03:04 AM, Jeff Moyer wrote: > Jens Axboe <axboe@...nel.dk> writes: > >> On 10/22/2015 09:53 AM, Jeff Moyer wrote: >>> I think that percolating BLK_MQ_F_TAG_SHARED up to the tag set would >>> allow newly created hctxs to simply inherit the shared state (in >>> blk_mq_init_hctx), and you won't need to freeze every queue in order to >>> guarantee that. >>> >>> I was writing a patch to that effect. I've now stopped as I want to >>> make sure I'm not off in the weeds. :) >> >> If that is where the delay is done, then yes, that should fix it and >> be a trivial patch. > > It's not quite as trivial as I had hoped. Jason, can you give the > attached patch a try? All I've done is boot tested it so far. > > Thanks! > Jeff > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 7785ae9..8b4c484 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1860,27 +1860,26 @@ static void blk_mq_map_swqueue(struct request_queue *q, > } > } > > -static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set) > +static void queue_set_hctx_shared(struct request_queue *q, bool shared) > { > struct blk_mq_hw_ctx *hctx; > - struct request_queue *q; > - bool shared; > int i; > > - if (set->tag_list.next == set->tag_list.prev) > - shared = false; > - else > - shared = true; > + queue_for_each_hw_ctx(q, hctx, i) { > + if (shared) > + hctx->flags |= BLK_MQ_F_TAG_SHARED; > + else > + hctx->flags &= ~BLK_MQ_F_TAG_SHARED; > + } > +} > + > +static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set, bool shared) > +{ > + struct request_queue *q; > > list_for_each_entry(q, &set->tag_list, tag_set_list) { > blk_mq_freeze_queue(q); > - > - queue_for_each_hw_ctx(q, hctx, i) { > - if (shared) > - hctx->flags |= BLK_MQ_F_TAG_SHARED; > - else > - hctx->flags &= ~BLK_MQ_F_TAG_SHARED; > - } > + queue_set_hctx_shared(q, shared); > blk_mq_unfreeze_queue(q); > } > } > @@ -1891,7 +1890,13 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q) > > mutex_lock(&set->tag_list_lock); > list_del_init(&q->tag_set_list); > - blk_mq_update_tag_set_depth(set); > + > + if (set->tag_list.next == set->tag_list.prev) { > + /* just transitioned to unshared */ > + set->flags &= ~BLK_MQ_F_TAG_SHARED; > + /* update existing queue */ > + blk_mq_update_tag_set_depth(set, false); > + } > mutex_unlock(&set->tag_list_lock); > } > > @@ -1902,7 +1907,24 @@ static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set, > > mutex_lock(&set->tag_list_lock); > list_add_tail(&q->tag_set_list, &set->tag_list); > - blk_mq_update_tag_set_depth(set); > + > + if (set->tag_list.next != set->tag_list.prev) { > + /* > + * Only update the tag set state if the state has > + * actually changed. > + */ > + if (!(set->flags & BLK_MQ_F_TAG_SHARED)) { > + /* just transitioned to shared tags */ > + set->flags |= BLK_MQ_F_TAG_SHARED; > + blk_mq_update_tag_set_depth(set, true); > + } else { > + /* ensure we didn't race with another addition */ > + struct blk_mq_hw_ctx *hctx = queue_first_hw_ctx(q); > + if ((hctx->flags & BLK_MQ_F_TAG_SHARED) != > + BLK_MQ_F_TAG_SHARED) > + queue_set_hctx_shared(q, true); > + } > + } > mutex_unlock(&set->tag_list_lock); > } > > diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h > index 5e7d43a..12ffc40 100644 > --- a/include/linux/blk-mq.h > +++ b/include/linux/blk-mq.h > @@ -254,6 +254,9 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq) > for ((i) = 0; (i) < (hctx)->nr_ctx && \ > ({ ctx = (hctx)->ctxs[(i)]; 1; }); (i)++) > > +#define queue_first_hw_ctx(q) \ > + (q)->queue_hw_ctx[0] > + > #define blk_ctx_sum(q, sum) \ > ({ \ > struct blk_mq_ctx *__x; \ > I tested with your patch which avoids looping all queues in set by checking flag BLK_MQ_F_TAG_SHARED. it works! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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