Messages in this thread Patch in this message | | | Subject | Re: [PATCH 2/2] blk-mq: sync the update nr_hw_queues with part_in_flight | From | "jianchao.wang" <> | Date | Thu, 16 Aug 2018 17:20:50 +0800 |
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Hi Ming
On 08/16/2018 05:03 PM, Ming Lei wrote: > diff --git a/block/blk-mq.c b/block/blk-mq.c > index b42a2c9ba00e..fbc5534f8178 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -113,6 +113,10 @@ void blk_mq_in_flight(struct request_queue *q, struct hd_struct *part, > struct mq_inflight mi = { .part = part, .inflight = inflight, }; > > inflight[0] = inflight[1] = 0; > + > + if (percpu_ref_is_dying(&q->q_usage_counter)) > + return; > + > blk_mq_queue_tag_busy_iter(q, blk_mq_check_inflight, &mi); > }
That's a good idea to use q->q_usage_counter. But I think we could do following modification: 1. use percpu_ref_is_zero, then we will not miss any in-flight request here. 2. use rcu to ensure the user of blk_mq_in_flight has gone out of the critical section.
Like following patch: diff --git a/block/blk-mq.c b/block/blk-mq.c index 89904cc..cd9878e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -113,7 +113,12 @@ void blk_mq_in_flight(struct request_queue *q, struct hd_struct *part, inflight[0] = inflight[1] = 0; + rcu_read_lock(); + if (percpu_ref_is_zero(&q->q_usage_counter)) + return; + blk_mq_queue_tag_busy_iter(q, blk_mq_check_inflight, &mi); + rcu_read_unlock(); } static void blk_mq_check_inflight_rw(struct blk_mq_hw_ctx *hctx, @@ -2907,6 +2912,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_freeze_queue(q); + synchronize_rcu(); /* * switch io scheduler to NULL to clean up the data in it. * will get it back after update mapping between cpu and hw queues. And also, some comment is needed to describe them. ;)
Thanks Jianchao
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