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Limit stripesize reported from nvd(4) to 4K

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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
This commit is contained in:
Steven Hartland 2015-12-11 02:06:03 +00:00
parent 777d81af62
commit fdf16a68ab
4 changed files with 36 additions and 1 deletions
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2
sys/dev/nvd/nvd.c
View File

@ -279,7 +279,7 @@ nvd_new_disk(struct nvme_namespace *ns, void *ctrlr_arg)
disk->d_sectorsize = nvme_ns_get_sector_size(ns);
disk->d_mediasize = (off_t)nvme_ns_get_size(ns);
disk->d_delmaxsize = (off_t)nvme_ns_get_size(ns);
disk->d_stripesize = nvme_ns_get_stripesize(ns);
disk->d_stripesize = nvme_ns_get_optimal_sector_size(ns);
if (TAILQ_EMPTY(&disk_head))
disk->d_unit = 0;

1
sys/dev/nvme/nvme.h
View File

@ -870,6 +870,7 @@ const char * nvme_ns_get_serial_number(struct nvme_namespace *ns);
const char * nvme_ns_get_model_number(struct nvme_namespace *ns);
const struct nvme_namespace_data *
nvme_ns_get_data(struct nvme_namespace *ns);
uint32_t nvme_ns_get_optimal_sector_size(struct nvme_namespace *ns);
uint32_t nvme_ns_get_stripesize(struct nvme_namespace *ns);
int nvme_ns_bio_process(struct nvme_namespace *ns, struct bio *bp,

18
sys/dev/nvme/nvme_ns.c
View File

@ -45,6 +45,8 @@ __FBSDID("$FreeBSD$");
#include "nvme_private.h"
extern int nvme_max_optimal_sectorsize;
static void nvme_bio_child_inbed(struct bio *parent, int bio_error);
static void nvme_bio_child_done(void *arg,
const struct nvme_completion *cpl);
@ -217,6 +219,22 @@ nvme_ns_get_stripesize(struct nvme_namespace *ns)
return (ns->stripesize);
}
uint32_t
nvme_ns_get_optimal_sector_size(struct nvme_namespace *ns)
{
uint32_t stripesize;
stripesize = nvme_ns_get_stripesize(ns);
if (stripesize == 0)
return nvme_ns_get_sector_size(ns);
if (nvme_max_optimal_sectorsize == 0)
return (stripesize);
return (MIN(stripesize, nvme_max_optimal_sectorsize));
}
static void
nvme_ns_bio_done(void *arg, const struct nvme_completion *status)
{

16
sys/dev/nvme/nvme_sysctl.c
View File

@ -33,6 +33,22 @@ __FBSDID("$FreeBSD$");
#include "nvme_private.h"
SYSCTL_NODE(_kern, OID_AUTO, nvme, CTLFLAG_RD, 0, "NVM Express");
/*
* 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 by default.
*
* 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.
*/
int nvme_max_optimal_sectorsize = 1<<12;
SYSCTL_INT(_kern_nvme, OID_AUTO, max_optimal_sectorsize, CTLFLAG_RWTUN,
&nvme_max_optimal_sectorsize, 0, "The maximum optimal sectorsize reported");
/*
* CTLTYPE_S64 and sysctl_handle_64 were added in r217616. Define these
* explicitly here for older kernels that don't include the r217616