On Fri, Apr 28, 2017 at 03:59:20PM +0000, Bart Van Assche wrote: > On Fri, 2017-04-28 at 07:42 -0600, Jens Axboe wrote: > > On 04/28/2017 01:32 AM, Ming Lei wrote: > > > We have freezed queue already, not necessary to call > > > blk_mq_quiesce_queue() any more, so remove it. > > > > Are you sure? It ensures that we also aren't in the middle of > > blk_mq_make_request(), we need a stable view of the sched > > status throughout that. > > Hello Jens, > > My understanding is that blk_mq_freeze_queue() provides stronger guarantees > than blk_mq_quiesce_queue(). The former waits until all pending requests have > finished while the latter only waits until pending .queue_rq() calls have > finished. blk_mq_freeze_queue() also causes new blk_get_request() calls to > wait until blk_mq_unfreeze_queue() is called while blk_get_request() can > still succeed after blk_mq_quiesce_queue() returned and before > blk_mq_start_stopped_hw_queues() is called. > > Regarding blk_mq_make_request(): I think that the blk_queue_enter() call in > generic_make_request() prevents that blk_mq_make_request() gets called after > a queue has been frozen. Jens & Bart, so I understand you don't object to this patch any more, then I will post a v1 for covering blk_mq_update_nr_requests(). Thanks, Ming
