On 01/27/2016 11:42 AM, Mike Snitzer wrote:
On Wed, Jan 27 2016 at 12:56pm -0500,
Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx> wrote:
On 27/01/2016 19:48, 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
$ for f in /sys/module/null_blk/parameters/*; do echo $f; cat $f; done
/sys/module/null_blk/parameters/bs
512
/sys/module/null_blk/parameters/completion_nsec
10000
/sys/module/null_blk/parameters/gb
250
/sys/module/null_blk/parameters/home_node
-1
/sys/module/null_blk/parameters/hw_queue_depth
64
/sys/module/null_blk/parameters/irqmode
1
/sys/module/null_blk/parameters/nr_devices
2
/sys/module/null_blk/parameters/queue_mode
2
/sys/module/null_blk/parameters/submit_queues
24
/sys/module/null_blk/parameters/use_lightnvm
N
/sys/module/null_blk/parameters/use_per_node_hctx
N
$ fio --group_reporting --rw=randread --bs=4k --numjobs=24
--iodepth=32 --runtime=99999999 --time_based --loops=1
--ioengine=libaio --direct=1 --invalidate=1 --randrepeat=1
--norandommap --exitall --name task_nullb0 --filename=/dev/nullb0
task_nullb0: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K,
ioengine=libaio, iodepth=32
...
fio-2.1.10
Starting 24 processes
Jobs: 24 (f=24): [rrrrrrrrrrrrrrrrrrrrrrrr] [0.0% done]
[7234MB/0KB/0KB /s] [1852K/0/0 iops] [eta 1157d:09h:46m:22s]
Thanks, the number of fio threads was pretty important. I'm still
seeing better IOPs with queue_mode=0 (bio-based).
Jobs: 24 (f=24): [r(24)] [11.7% done] [11073MB/0KB/0KB /s] [2835K/0/0 iops] [eta 14m:42s]
(with queue_mode=2 I get ~1930K IOPs.. which I need to use to stack
request-based DM multipath ontop)
Now I can focus on why dm-multipath is slow...
queue_mode=0 doesn't do a whole lot, once you add the required bits for
a normal driver, that will eat up a bit of overhead. The point was to
retain scaling, and to avoid drivers having to built support for the
required functionality from scratch. If we do that once and
fast/correct, then all mq drivers get it.
That said, your jump is a big one. Some of that is support
functionality, and some of it (I bet) is just doing io stats. If you
disable io stats with queue_mode=2, the performance will most likely
increase. Other things we just can't disable or don't want to disable,
if we are going to keep this as an indication of what a real driver
could do through the mq stack.
Now, if queue_mode=1 is faster, then there's certainly an issue!
--
Jens Axboe
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