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D4446.1775691614.diff
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D4446.1775691614.diff
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Index: sys/dev/nvd/nvd.c
===================================================================
--- sys/dev/nvd/nvd.c
+++ sys/dev/nvd/nvd.c
@@ -32,6 +32,7 @@
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
+#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/taskqueue.h>
@@ -58,6 +59,22 @@
MALLOC_DEFINE(M_NVD, "nvd", "nvd(4) allocations");
+SYSCTL_NODE(_kern, OID_AUTO, nvd, CTLFLAG_RD, 0, "NVM Express disk driver");
+/*
+ * 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.
+ */
+static int nvd_max_stripesize = 1<<12;
+SYSCTL_INT(_kern_nvd, OID_AUTO, max_stripsize, CTLFLAG_RWTUN,
+ &nvd_max_stripesize, 0, "The maximum stripe size reported to geom(8)");
+
struct nvme_consumer *consumer_handle;
struct nvd_disk {
@@ -279,7 +296,9 @@
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 = nvd_max_stripesize == 0 ?
+ nvme_ns_get_stripesize(ns) :
+ MIN(nvme_ns_get_stripesize(ns), nvd_max_stripesize);
if (TAILQ_EMPTY(&disk_head))
disk->d_unit = 0;

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