On Thu, 2019-04-04 at 07:59 -0700, Bart Van Assche wrote: > On Thu, 2019-04-04 at 15:08 +0800, Ming Lei wrote: > > On Wed, Apr 03, 2019 at 01:11:26PM -0700, Bart Van Assche wrote: > > > If blk_mq_try_issue_directly() returns BLK_STS*_RESOURCE that > > > means that > > > the request has not been queued and that the caller should retry > > > to submit > > > the request. Both blk_mq_request_bypass_insert() and > > > blk_mq_sched_insert_request() guarantee that a request will be > > > processed. > > > Hence return BLK_STS_OK if one of these functions is called. This > > > patch > > > avoids that blk_mq_dispatch_rq_list() crashes when using dm- > > > mpath. > > > > > > Cc: Christoph Hellwig <[email protected]> > > > Cc: Hannes Reinecke <[email protected]> > > > Cc: James Smart <[email protected]> > > > Cc: Ming Lei <[email protected]> > > > Cc: Jianchao Wang <[email protected]> > > > Cc: Keith Busch <[email protected]> > > > Cc: Dongli Zhang <[email protected]> > > > Cc: Laurence Oberman <[email protected]> > > > Tested-by: Laurence Oberman <[email protected]> > > > Reviewed-by: Laurence Oberman <[email protected]> > > > Reported-by: Laurence Oberman <[email protected]> > > > Fixes: 7f556a44e61d ("blk-mq: refactor the code of issue request > > > directly") # v5.0. > > > Cc: <[email protected]> > > > Signed-off-by: Bart Van Assche <[email protected]> > > > --- > > > block/blk-mq.c | 9 ++------- > > > 1 file changed, 2 insertions(+), 7 deletions(-) > > > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > > index 652d0c6d5945..b2c20dce8a30 100644 > > > --- a/block/blk-mq.c > > > +++ b/block/blk-mq.c > > > @@ -1859,16 +1859,11 @@ blk_status_t > > > blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, > > > case BLK_STS_RESOURCE: > > > if (force) { > > > blk_mq_request_bypass_insert(rq, run_queue); > > > - /* > > > - * We have to return BLK_STS_OK for the DM > > > - * to avoid livelock. Otherwise, we return > > > - * the real result to indicate whether the > > > - * request is direct-issued successfully. > > > - */ > > > - ret = bypass ? BLK_STS_OK : ret; > > > + ret = BLK_STS_OK; > > > } else if (!bypass) { > > > blk_mq_sched_insert_request(rq, false, > > > run_queue, false); > > > + ret = BLK_STS_OK; > > > } > > > > This change itself is correct. > > > > However, there is other issue introduced by 7f556a44e61d. > > > > We need blk_insert_cloned_request() to pass back > > BLK_STS_RESOURCE/BLK_STS_RESOURCE > > to caller, so that dm-rq driver may see the underlying queue is > > busy, then tell > > blk-mq to deal with the busy condition from dm-rq queue, so that IO > > merge can get improved. > > > > That is exactly what 396eaf21ee17c476e8f6 ("blk-mq: improve DM's > > blk-mq IO merging > > via blk_insert_cloned_request feedback") did. > > > > There must be performance regression with 7f556a44e61d by cut the > > feedback. > > > > So could you fix them all in one patch? > > Since commit 7f556a44e61d introduced multiple problems and since > fixing > these is nontrivial, how about reverting that commit? > > Thanks, > > Bart.
When I bisected and got to that commit I was unable to revert it to test without it. I showed that in an earlier update, had merge issues. loberman@lobewsrhel linux_torvalds]$ git revert 7f556a44e61d error: could not revert 7f556a4... blk-mq: refactor the code of issue request directly hint: after resolving the conflicts, mark the corrected paths hint: with 'git add <paths>' or 'git rm <paths>' hint: and commit the result with 'git commit'
