On Wed, Jan 27 2016 at 6:14am -0500, Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx> wrote: > > >>I don't think this is going to help __multipath_map() without some > >>configuration changes. Now that we're running on already merged > >>requests instead of bios, the m->repeat_count is almost always set to 1, > >>so we call the path_selector every time, which means that we'll always > >>need the write lock. Bumping up the number of IOs we send before calling > >>the path selector again will give this patch a change to do some good > >>here. > >> > >>To do that you need to set: > >> > >> rr_min_io_rq <something_bigger_than_one> > >> > >>in the defaults section of /etc/multipath.conf and then reload the > >>multipathd service. > >> > >>The patch should hopefully help in multipath_busy() regardless of the > >>the rr_min_io_rq setting. > > > >This patch, while generic, is meant to help the blk-mq case. A blk-mq > >request_queue doesn't have an elevator so the requests will not have > >seen merging. > > > >But yes, implied in the patch is the requirement to increase > >m->repeat_count via multipathd's rr_min_io_rq (I'll backfill a proper > >header once it is tested). > > I'll test it once I get some spare time (hopefully soon...) OK thanks. BTW, I _cannot_ get null_blk to come even close to your reported 1500K+ IOPs on 2 "fast" systems I have access to. Which arguments are you loading the null_blk module with? I've been using: modprobe null_blk gb=4 bs=4096 nr_devices=1 queue_mode=2 submit_queues=12 On my 1 system is a 12 core single socket, single NUMA node with 12G of memory, I can only get ~500K read IOPs and ~85K write IOPs. On another much larger system with 72 cores and 4 NUMA nodes with 128G of memory, I can only get ~310K read IOPs and ~175K write IOPs. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
