On Mon, Jan 15 2018 at 11:58am -0500, Ming Lei <ming.lei@xxxxxxxxxx> wrote: > blk_insert_cloned_request() is called in fast path of dm-rq driver, and > in this function we append request to hctx->dispatch_list of the underlying > queue directly. > > 1) This way isn't efficient enough because hctx lock is always required > > 2) With blk_insert_cloned_request(), we bypass underlying queue's IO scheduler > totally, and depend on DM rq driver to do IO schedule completely. But DM > rq driver can't get underlying queue's dispatch feedback at all, and this > information is extreamly useful for IO merge. Without that IO merge can't > be done basically by blk-mq, and causes very bad sequential IO performance. > > This patch makes use of blk_mq_try_issue_directly() to dispatch rq to > underlying queue and provides disptch result to dm-rq and blk-mq, and > improves the above situations very much. > > With this patch, seqential IO is improved by 3X in my test over > mpath/virtio-scsi. > > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > --- > block/blk-mq.c | 29 ++++++++++++++++++++++++++--- > 1 file changed, 26 insertions(+), 3 deletions(-) Hey Ming, I also just noticed your V4 of this patch only includes the block/blk-mq.c changes. You're missing: block/blk-core.c | 3 +-- block/blk-mq.h | 3 +++ drivers/md/dm-rq.c | 19 +++++++++++++--- Please let Jens know if you're OK with my V4, tagged here: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/tag/?h=for-block-4.16/dm-changes-2 And also detailed in this message from earlier in this thread: https://marc.info/?l=linux-block&m=151603824725438&w=2 Or please generate V5 of your series. Hopefully it'd include the header I revised for this 3/3 patch, see: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-block-4.16/dm-changes-2&id=d86beab5712a8f18123011487dee797a1e3a07e1 We also need to address the issues Jens noticed and I looked at a bit closer: https://marc.info/?l=linux-block&m=151604528127707&w=2 (those issues might need fixing first, and marked for stable@, and the series rebased ontop of it?) Thanks! Mie
