svn commit: r292074 - in head/sys/dev: nvd nvme

[Alan Somers]

Are you saying that Intel NVMe controllers perform poorly for all I/Os that
are less than 128KB, or just for I/Os of any size that cross a 128KB
boundary?

On Thu, Dec 10, 2015 at 7:06 PM, Steven Hartland <smh at freebsd.org> wrote:

> Author: smh
> Date: Fri Dec 11 02:06:03 2015
> New Revision: 292074
> URL: https://svnweb.freebsd.org/changeset/base/292074
>
> Log:
>   Limit stripesize reported from nvd(4) to 4K
>
>   Intel NVMe controllers have a slow path for I/Os that span a 128KB
> stripe boundary but ZFS limits ashift, which is derived from d_stripesize,
> to 13 (8KB) so we limit the stripesize reported to geom(8) to 4KB.
>
>   This may result in a small number of additional I/Os to require
> splitting in nvme(4), however the NVMe I/O path is very efficient so these
> additional I/Os will cause very minimal (if any) difference in performance
> or CPU utilisation.
>
>   This can be controller by the new sysctl
> kern.nvme.max_optimal_sectorsize.
>
>   MFC after:    1 week
>   Sponsored by: Multiplay
>   Differential Revision:        https://reviews.freebsd.org/D4446
>
> Modified:
>   head/sys/dev/nvd/nvd.c
>   head/sys/dev/nvme/nvme.h
>   head/sys/dev/nvme/nvme_ns.c
>   head/sys/dev/nvme/nvme_sysctl.c
>
>