Re: [PATCH 1/3] nvme/pci: Start request after doorbell ring

Keith Busch
2018-01-23T00:16:29Z

On Wed, Jan 03, 2018 at 01:21:05PM -0700, Keith Busch wrote:
>
> I've removed the submission side poll in a local build, and amazingly I
> am observing a not insignificant increase in latency without it on some
> workloads with certain hardware. I will have to delay recommending/posting
> removal of this pending further investigation.

This took longer to narrow than I hoped. I had been getting very wild
results, and there were two things to blame: a kernel irq issue[*],
and a platform bios causing a lot of CPU thermal frequency throttling.

Now that's sorted out, I am back to tuning this and the opprotunistic
nvme submission side polling once again does not produce a measurable
difference. My world is sane again. Will try to send an update for
consideration this week after some more testing.

* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=a0c9259dc4