On Fri, Apr 07 2017 at 2:16pm -0400, Bart Van Assche <bart.vanassche@xxxxxxxxxxx> wrote: > While running the srp-test software I noticed that request > processing stalls sporadically at the beginning of a test, namely > when mkfs is run against a dm-mpath device. Every time when that > happened the following command was sufficient to resume request > processing: > > echo run >/sys/kernel/debug/block/dm-0/state > > This patch avoids that such request processing stalls occur. The > test I ran is as follows: > > while srp-test/run_tests -d -r 30 -t 02-mq; do :; done > > Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx> > Cc: Mike Snitzer <snitzer@xxxxxxxxxx> > Cc: dm-devel@xxxxxxxxxx > --- > drivers/md/dm-rq.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c > index 6886bf160fb2..d19af1d21f4c 100644 > --- a/drivers/md/dm-rq.c > +++ b/drivers/md/dm-rq.c > @@ -755,6 +755,7 @@ static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx, > /* Undo dm_start_request() before requeuing */ > rq_end_stats(md, rq); > rq_completed(md, rq_data_dir(rq), false); > + blk_mq_delay_run_hw_queue(hctx, 100/*ms*/); > return BLK_MQ_RQ_QUEUE_BUSY; > } > > -- > 2.12.0 > I really appreciate your hard work Bart but this looks like a cheap hack. I'm clearly too late to stop this from going in (given Jens got it merged for -rc6) but: this has no place in dm-mq (or any blk-mq driver). If it is needed it should be elevated to blk-mq core to trigger blk_mq_delay_run_hw_queue() when BLK_MQ_RQ_QUEUE_BUSY is returned from blk_mq_ops' .queue_rq. If this dm-mq specific commit is justified the case certainly is spelled out in the commit header.
