On 01/27/2016 10:48 AM, 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
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).
--
Jens Axboe
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
