222 lines
6.8 KiB
Groff
222 lines
6.8 KiB
Groff
.\"
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.\" Copyright (c) 2012-2016 Intel Corporation
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions, and the following disclaimer,
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.\" without modification.
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.\" 2. Redistributions in binary form must reproduce at minimum a disclaimer
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.\" substantially similar to the "NO WARRANTY" disclaimer below
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.\" ("Disclaimer") and any redistribution must be conditioned upon
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.\" including a substantially similar Disclaimer requirement for further
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.\" binary redistribution.
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.\"
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.\" NO WARRANTY
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
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.\" A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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.\" HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
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.\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGES.
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.\"
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.\" nvme driver man page.
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.\"
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.\" Author: Jim Harris <jimharris@FreeBSD.org>
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 18, 2019
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.Dt NVME 4
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.Os
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.Sh NAME
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.Nm nvme
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.Nd NVM Express core driver
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.Sh SYNOPSIS
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To compile this driver into your kernel,
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place the following line in your kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device nvme"
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.Ed
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.Pp
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Or, to load the driver as a module at boot, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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nvme_load="YES"
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.Ed
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.Pp
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Most users will also want to enable
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.Xr nvd 4
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to expose NVM Express namespaces as disk devices which can be
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partitioned.
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Note that in NVM Express terms, a namespace is roughly equivalent to a
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SCSI LUN.
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.Sh DESCRIPTION
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The
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.Nm
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driver provides support for NVM Express (NVMe) controllers, such as:
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.Bl -bullet
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.It
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Hardware initialization
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.It
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Per-CPU IO queue pairs
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.It
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API for registering NVMe namespace consumers such as
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.Xr nvd 4
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or
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.Xr nda 4
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.It
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API for submitting NVM commands to namespaces
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.It
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Ioctls for controller and namespace configuration and management
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.El
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.Pp
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The
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.Nm
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driver creates controller device nodes in the format
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.Pa /dev/nvmeX
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and namespace device nodes in
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the format
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.Pa /dev/nvmeXnsY .
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Note that the NVM Express specification starts numbering namespaces at 1,
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not 0, and this driver follows that convention.
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.Sh CONFIGURATION
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By default,
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.Nm
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will create an I/O queue pair for each CPU, provided enough MSI-X vectors
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and NVMe queue pairs can be allocated.
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If not enough vectors or queue
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pairs are available, nvme(4) will use a smaller number of queue pairs and
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assign multiple CPUs per queue pair.
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.Pp
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To force a single I/O queue pair shared by all CPUs, set the following
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tunable value in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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hw.nvme.per_cpu_io_queues=0
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.Ed
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.Pp
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To assign more than one CPU per I/O queue pair, thereby reducing the number
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of MSI-X vectors consumed by the device, set the following tunable value in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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hw.nvme.min_cpus_per_ioq=X
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.Ed
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.Pp
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To force legacy interrupts for all
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.Nm
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driver instances, set the following tunable value in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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hw.nvme.force_intx=1
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.Ed
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.Pp
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Note that use of INTx implies disabling of per-CPU I/O queue pairs.
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.Pp
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The
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.Xr nvd 4
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driver is used to provide a disk driver to the system by default.
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The
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.Xr nda 4
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driver can also be used instead.
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The
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.Xr nvd 4
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driver performs better with smaller transactions and few TRIM
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commands.
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It sends all commands directly to the drive immediately.
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The
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.Xr nda 4
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driver performs better with larger transactions and also collapses
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TRIM commands giving better performance.
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It can queue commands to the drive; combine
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.Dv BIO_DELETE
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commands into a single trip; and
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use the CAM I/O scheduler to bias one type of operation over another.
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To select the
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.Xr nda 4
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driver, set the following tunable value in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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hw.nvme.use_nvd=0
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.Ed
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.Pp
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This value may also be set in the kernel config file with
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.Bd -literal -offset indent
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.Cd options NVME_USE_NVD=0
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.Ed
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.Sh SYSCTL VARIABLES
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The following controller-level sysctls are currently implemented:
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.Bl -tag -width indent
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.It Va dev.nvme.0.num_cpus_per_ioq
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(R) Number of CPUs associated with each I/O queue pair.
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.It Va dev.nvme.0.int_coal_time
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(R/W) Interrupt coalescing timer period in microseconds.
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Set to 0 to disable.
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.It Va dev.nvme.0.int_coal_threshold
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(R/W) Interrupt coalescing threshold in number of command completions.
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Set to 0 to disable.
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.El
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.Pp
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The following queue pair-level sysctls are currently implemented.
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Admin queue sysctls take the format of dev.nvme.0.adminq and I/O queue sysctls
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take the format of dev.nvme.0.ioq0.
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.Bl -tag -width indent
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.It Va dev.nvme.0.ioq0.num_entries
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(R) Number of entries in this queue pair's command and completion queue.
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.It Va dev.nvme.0.ioq0.num_tr
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(R) Number of nvme_tracker structures currently allocated for this queue pair.
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.It Va dev.nvme.0.ioq0.num_prp_list
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(R) Number of nvme_prp_list structures currently allocated for this queue pair.
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.It Va dev.nvme.0.ioq0.sq_head
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(R) Current location of the submission queue head pointer as observed by
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the driver.
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The head pointer is incremented by the controller as it takes commands off
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of the submission queue.
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.It Va dev.nvme.0.ioq0.sq_tail
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(R) Current location of the submission queue tail pointer as observed by
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the driver.
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The driver increments the tail pointer after writing a command
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into the submission queue to signal that a new command is ready to be
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processed.
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.It Va dev.nvme.0.ioq0.cq_head
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(R) Current location of the completion queue head pointer as observed by
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the driver.
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The driver increments the head pointer after finishing
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with a completion entry that was posted by the controller.
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.It Va dev.nvme.0.ioq0.num_cmds
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(R) Number of commands that have been submitted on this queue pair.
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.It Va dev.nvme.0.ioq0.dump_debug
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(W) Writing 1 to this sysctl will dump the full contents of the submission
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and completion queues to the console.
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.El
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.Sh SEE ALSO
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.Xr nda 4 ,
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.Xr nvd 4 ,
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.Xr pci 4 ,
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.Xr nvmecontrol 8 ,
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.Xr disk 9
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 9.2 .
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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driver was developed by Intel and originally written by
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.An Jim Harris Aq Mt jimharris@FreeBSD.org ,
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with contributions from
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.An Joe Golio
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at EMC.
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.Pp
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This man page was written by
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.An Jim Harris Aq Mt jimharris@FreeBSD.org .
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