On Sat, Jun 20, 2020 at 07:14:51AM +0800, Ming Lei wrote: > On Fri, Jun 19, 2020 at 07:04:05PM -0400, Mike Snitzer wrote: > > On Fri, Jun 19 2020 at 6:52pm -0400, > > Ming Lei <[email protected]> wrote: > > > > > On Sat, Jun 20, 2020 at 06:37:44AM +0800, Ming Lei wrote: > > > > On Fri, Jun 19, 2020 at 01:40:41PM -0400, Mike Snitzer wrote: > > > > > On Fri, Jun 19 2020 at 12:06pm -0400, > > > > > Mike Snitzer <[email protected]> wrote: > > > > > > > > > > > On Fri, Jun 19 2020 at 6:11am -0400, > > > > > > Ming Lei <[email protected]> wrote: > > > > > > > > > > > > > Hi Mike, > > > > > > > > > > > > > > On Fri, Jun 19, 2020 at 05:42:50AM -0400, Mike Snitzer wrote: > > > > > > > > Hi Ming, > > > > > > > > > > > > > > > > Thanks for the patch! But I'm having a hard time understanding > > > > > > > > what > > > > > > > > you've written in the patch header, > > > > > > > > > > > > > > > > On Fri, Jun 19 2020 at 4:42am -0400, > > > > > > > > Ming Lei <[email protected]> wrote: > > > > > > > > > > > > > > > > > dm-rq won't stop queue, meantime blk-mq won't stop one queue > > > > > > > > > too, so > > > > > > > > > remove the check. > > > > > > > > > > > > > > > > It'd be helpful if you could unpack this with more detail > > > > > > > > before going on > > > > > > > > to explain why using blk_queue_quiesced, despite dm-rq using > > > > > > > > blk_mq_queue_stopped, would also be ineffective. > > > > > > > > > > > > > > > > SO: > > > > > > > > > > > > > > > > > dm-rq won't stop queue > > > > > > > > > > > > > > > > 1) why won't dm-rq stop the queue? Do you mean it won't > > > > > > > > reliably > > > > > > > > _always_ stop the queue because of the > > > > > > > > blk_mq_queue_stopped() check? > > > > > > > > > > > > > > device mapper doesn't call blk_mq_stop_hw_queue or > > > > > > > blk_mq_stop_hw_queues. > > > > > > > > > > > > > > > > > > > > > > > > meantime blk-mq won't stop one queue too, so remove the check. > > > > > > > > > > > > > > > > 2) Meaning?: blk_mq_queue_stopped() will return true even if > > > > > > > > only one hw > > > > > > > > queue is stopped, given blk-mq must stop all hw queues a > > > > > > > > positive return > > > > > > > > from this blk_mq_queue_stopped() check is incorrectly assuming > > > > > > > > it meanss > > > > > > > > all hw queues are stopped. > > > > > > > > > > > > > > blk-mq won't call blk_mq_stop_hw_queue or blk_mq_stop_hw_queues > > > > > > > for > > > > > > > dm-rq's queue too, so dm-rq's hw queue won't be stopped. > > > > > > > > > > > > > > BTW blk_mq_stop_hw_queue or blk_mq_stop_hw_queues are supposed to > > > > > > > be > > > > > > > used for throttling queue. > > > > > > > > > > > > I'm going to look at actually stopping the queue (using one of these > > > > > > interfaces). I didn't realize I wasn't actually stopping the queue. > > > > > > The intent was to do so. > > > > > > > > > > > > In speaking with Jens yesterday about freeze vs stop: it is clear > > > > > > that > > > > > > dm-rq needs to still be able to allocate new requests, but _not_ > > > > > > call > > > > > > the queue_rq to issue the requests, while "stopped" (due to dm-mpath > > > > > > potentially deferring retries of failed requests because of path > > > > > > failure > > > > > > while quiescing the queue during DM device suspend). But that > > > > > > freezing > > > > > > the queue goes too far because it won't allow such request > > > > > > allocation. > > > > > > > > > > Seems I'm damned if I do (stop) or damned if I don't (new reports of > > > > > requests completing after DM device suspend's > > > > > blk_mq_quiesce_queue()+dm_wait_for_completion()). > > > > > > > > request(but not new) completing is possible after > > > > blk_mq_quiesce_queue()+ > > > > dm_wait_for_completion, because blk_mq_rq_inflight() only checks > > > > INFLIGHT > > > > request. If all requests are marked as MQ_RQ_COMPLETE, > > > > blk_mq_rq_inflight() > > > > still may return false. However, MQ_RQ_COMPLETE is one transient state. > > > > > > > > So what does dm-rq expect from dm_wait_for_completion()? > > > > > > > > If it is just no new request entering dm_queue_rq(), there shouldn't be > > > > issue. > > > > > > > > If dm-rq hopes there aren't any real inflight request(MQ_RQ_COMPLETE & > > > > MQ_RQ_INFLIGHT), we can change blk_mq_rq_inflight to support that. > > > > > > Hi Mike, > > > > > > Please test the following patch and see if the issue can be fixed: > > > > > > From faf0f9f15627446e8c35db518e37a4a2e4323eb2 Mon Sep 17 00:00:00 2001 > > > From: Ming Lei <[email protected]> > > > Date: Sat, 20 Jun 2020 06:45:49 +0800 > > > Subject: [PATCH] blk-mq: cover request of MQ_RQ_COMPLETE as inflight in > > > blk_mq_rq_inflight > > > > > > When request is marked as MQ_RQ_COMPLETE, ->complete isn't called & done > > > yet, and driver may expect that there isn't any driver related activity > > > since > > > blk_mq_queue_inflight() returns. > > > > > > Fixes it by covering request of MQ_RQ_COMPLETE as inflight in > > > blk_mq_rq_inflight(). > > > > > > Cc: Mike Snitzer <[email protected]> > > > Signed-off-by: Ming Lei <[email protected]> > > > --- > > > block/blk-mq.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > > index 4f57d27bfa73..7bc084b5bc37 100644 > > > --- a/block/blk-mq.c > > > +++ b/block/blk-mq.c > > > @@ -831,7 +831,7 @@ static bool blk_mq_rq_inflight(struct blk_mq_hw_ctx > > > *hctx, struct request *rq, > > > * If we find a request that is inflight and the queue matches, > > > * we know the queue is busy. Return false to stop the iteration. > > > */ > > > - if (rq->state == MQ_RQ_IN_FLIGHT && rq->q == hctx->queue) { > > > + if (rq->state != MQ_RQ_IDLE && rq->q == hctx->queue) { > > > bool *busy = priv; > > > > > > *busy = true; > > > -- > > > 2.25.2 > > > > > > > I was going to ask if being more explit would be better: > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > index 4f57d27bfa73..96816ce57eb1 100644 > > --- a/block/blk-mq.c > > +++ b/block/blk-mq.c > > @@ -828,10 +828,11 @@ static bool blk_mq_rq_inflight(struct blk_mq_hw_ctx > > *hctx, struct request *rq, > > void *priv, bool reserved) > > { > > /* > > - * If we find a request that is inflight and the queue matches, > > + * If we find a request that is inflight or complete and the queue > > matches, > > * we know the queue is busy. Return false to stop the iteration. > > */ > > - if (rq->state == MQ_RQ_IN_FLIGHT && rq->q == hctx->queue) { > > + if ((rq->state == MQ_RQ_IN_FLIGHT || rq->state == MQ_RQ_COMPLETE) > > && > > + rq->q == hctx->queue) { > > bool *busy = priv; > > > > *busy = true; > > > > But is your patch more forgiving of any future blk-mq states that might > > also consistitute outstanding work? Seems likely. > > I am fine with either way since it is called in slow path.
BTW, another candidate is to use blk_mq_request_started(). Thanks, Ming -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
