On 11/16/2016 10:31 AM, Stephen Bates wrote:
On Fri, November 11, 2016 11:11 pm, Jens Axboe wrote:
Respun on top of for-4.10/block, dropping patches that have been
merged. This patchset adds Christoph's simplified sync O_DIRECT bdev access
mode, and implements a more efficient IO polling on top of it. For more
details, see the v2 posting here:
http://www.mail-archive.com/linux-block@xxxxxxxxxxxxxxx/msg02079.html
Changes since v2:
- Adapt to blk stat changes
- Make it explicit that only blk-mq supports polling
- Fix a bug in the hrtimer code, switching to absolute mode if we
have to loop around (thanks Omar).
Hi Jens
I applied this series cleanly on top of 2868f13c303e147 in your
for-4.10/block branch. I tested using a simple fio wrapper script [1] on a
low-latency NVMe SSD [2]. Here are some results:
io_poll io_poll_delay threads latency CPU/threads
0 N/A 1 17.0 47%
1 -1 1 13.8 100%
1 0 1 14.6 73%
1 10 1 17.0 56%
0 N/A 8 18.7 47%
1 -1 8 14.4 100%
1 0 8 15.7 73%
1 10 8 19.0 56%
The io_poll_delay option 0 is definitely a nice compromise between no
polling and 100% polling. The result for io_poll_delay=10us is interesting
as it implies there might be some mismatch between that value and the
completion time. However I think that is something we can improve on over
time and I don't see it as a reason to not get this series upstream.
For the series:
Tested-By: Stephen Bates <sbates@xxxxxxxxxxxx>
Reviewed-By: Stephen Bates <sbates@xxxxxxxxxxxx>
Thanks for testing, Stephen, I'll add your tested/reviewed-by tags. As
to the specific setting of the time, it might just be that it's a poor
choice of value. We'll need some time to setup the delay, and if we end
up being late, then we'll make things worse. But I agree, we can look
into that going forward. I've got some more ideas on how to improve the
timing in general, so we can both get closer to -1 and get better
efficiency as well.
--
Jens Axboe
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