freebsd-nq/sys/dev/nvd
Steven Hartland fdf16a68ab 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
2015-12-11 02:06:03 +00:00
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nvd.c Limit stripesize reported from nvd(4) to 4K 2015-12-11 02:06:03 +00:00