Hi Mike,
So I gave your patches a go (dm-4.6) but I still don't see the
improvement you reported (while I do see a minor improvement).
null_blk queue_mode=2 submit_queues=24
dm_mod blk_mq_nr_hw_queues=24 blk_mq_queue_depth=4096 use_blk_mq=Y
I see 620K IOPs on dm_mq vs. 1750K IOPs on raw nullb0.
blk_mq_nr_hw_queues=24 isn't likely to help you (but with these patches,
the first being the most important, it shouldn't hurt either provided
you have 24 cpus).
I tried with less but as you said, it didn't have an impact...
Could be you have multiple NUMA nodes and are seeing problems from that?
I am running on a dual socket server, this can most likely be the
culprit...
I have 12 cpus (in the same physical cpu) and only a single NUMA node.
I get the same results as blk_mq_nr_hw_queues=12 with
blk_mq_nr_hw_queues=4 (same goes for null_blk submit_queues).
I've seen my IOPs go from ~950K to ~1400K. The peak null_blk can get on
my setup is ~1950K. So I'm still seeing a ~25% drop with dm-mq (but
that is much better than the over 50% drop I saw seeing).
That's what I was planning on :(
Is there something I'm missing?
Not sure, I just emailed out all my patches (and cc'd you). Please
verify you're using the latest here (same as 'dm-4.6' branch):
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=for-next
I rebased a couple times... so please diff what you have tested against
this latest 'dm-4.6' branch.
I am. I'll try to instrument what's going on...
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