On Wed, Jan 27 2016 at 1:26pm -0500, Jens Axboe <axboe@xxxxxxxxx> wrote: > On 01/27/2016 11:16 AM, Mike Snitzer wrote: > >On Wed, Jan 27 2016 at 12:51pm -0500, > >Jens Axboe <axboe@xxxxxxxxx> wrote: > > > >>On 01/27/2016 10:48 AM, Mike Snitzer wrote: > >>> > >>>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. > >> > >>Look at the completion method (irqmode) and completion time > >>(completion_nsec). > > > >OK, I found that queue_mode=0 (bio-based) is _much_ faster than blk-mq > >(2, the default). Improving to ~950K read IOPs and ~675K write IOPs (on > >the single numa node system). > > > >Default for irqmode is 1 (softirq). 2 (timer) yields poor results. 0 > >(none) seems slightly slower than 1. > > > >And if I use completion_nsec=1 I can bump up to ~990K read IOPs. > > > >Seems the best, for IOPs, so far on this system is with: > >modprobe null_blk gb=4 bs=4096 nr_devices=1 queue_mode=0 irqmode=1 completion_nsec=1 submit_queues=4 > > That sounds a bit odd. queue_mode=0 will always be a bit faster, > depending on how many threads, etc. But from 310K to 950K, that > sounds very suspicious. I definitely see much better results with bio-based over blk-mq. For the multithreaded fio job Sagi shared I'm seeing bio-based ~2835K vs blk-mq ~1950K (read IOPs). > And 500K/85K read/write is very low. Just did a quickie on a 2 node > box I have here, single thread performance with queue_mode=2 is > around 500K/500K read/write. Yeah, I was using some crap ioping test to get those 500K/85K results. I've now switched to the fio test Sagi shared and am seeing: ~1950K IOPs with blk-mq nullb0, only ~310K with .request_fn dm-mpath ontop, and ~955K with blk-mq dm-mpath ontop -- all read IOPs. So at least now I can get my eye back on the prize of improving blk-mq dm-multipath! -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
