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 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
