Some Intel NVMe drives behave badly when the LBA range crosses a 128k boundary. Their performance is worse for those transactions than for ones that don't cross the 128k boundary.
Warner On Thu, Mar 10, 2016 at 11:01 AM, Alan Somers <asom...@freebsd.org> wrote: > 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 <s...@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 >> >> _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
