On 27/01/2016 19:48, Mike Snitzer wrote:
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
$ 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]
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