.\" .\" Copyright (c) 2012-2016 Intel Corporation .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions, and the following disclaimer, .\" without modification. .\" 2. Redistributions in binary form must reproduce at minimum a disclaimer .\" substantially similar to the "NO WARRANTY" disclaimer below .\" ("Disclaimer") and any redistribution must be conditioned upon .\" including a substantially similar Disclaimer requirement for further .\" binary redistribution. .\" .\" NO WARRANTY .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS .\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT .\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR .\" A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT .\" HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING .\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGES. .\" .\" nvme driver man page. .\" .\" Author: Jim Harris .\" .\" $FreeBSD: releng/12.2/share/man/man4/nvme.4 365530 2020-09-09 22:33:11Z imp $ .\" .Dd June 6, 2020 .Dt NVME 4 .Os .Sh NAME .Nm nvme .Nd NVM Express core driver .Sh SYNOPSIS To compile this driver into your kernel, place the following line in your kernel configuration file: .Bd -ragged -offset indent .Cd "device nvme" .Ed .Pp Or, to load the driver as a module at boot, place the following line in .Xr loader.conf 5 : .Bd -literal -offset indent nvme_load="YES" .Ed .Pp Most users will also want to enable .Xr nvd 4 or .Xr nda 4 to expose NVM Express namespaces as disk devices which can be partitioned. Note that in NVM Express terms, a namespace is roughly equivalent to a SCSI LUN. .Sh DESCRIPTION The .Nm driver provides support for NVM Express (NVMe) controllers, such as: .Bl -bullet .It Hardware initialization .It Per-CPU IO queue pairs .It API for registering NVMe namespace consumers such as .Xr nvd 4 or .Xr nda 4 .It API for submitting NVM commands to namespaces .It Ioctls for controller and namespace configuration and management .El .Pp The .Nm driver creates controller device nodes in the format .Pa /dev/nvmeX and namespace device nodes in the format .Pa /dev/nvmeXnsY . Note that the NVM Express specification starts numbering namespaces at 1, not 0, and this driver follows that convention. .Sh CONFIGURATION By default, .Nm will create an I/O queue pair for each CPU, provided enough MSI-X vectors and NVMe queue pairs can be allocated. If not enough vectors or queue pairs are available, nvme(4) will use a smaller number of queue pairs and assign multiple CPUs per queue pair. .Pp To force a single I/O queue pair shared by all CPUs, set the following tunable value in .Xr loader.conf 5 : .Bd -literal -offset indent hw.nvme.per_cpu_io_queues=0 .Ed .Pp To assign more than one CPU per I/O queue pair, thereby reducing the number of MSI-X vectors consumed by the device, set the following tunable value in .Xr loader.conf 5 : .Bd -literal -offset indent hw.nvme.min_cpus_per_ioq=X .Ed .Pp To force legacy interrupts for all .Nm driver instances, set the following tunable value in .Xr loader.conf 5 : .Bd -literal -offset indent hw.nvme.force_intx=1 .Ed .Pp Note that use of INTx implies disabling of per-CPU I/O queue pairs. .Pp To control maximum amount of system RAM in bytes to use as Host Memory Buffer for capable devices, set the following tunable: .Bd -literal -offset indent hw.nvme.hmb_max .Ed .Pp The default value is 5% of physical memory size per device. .Pp The .Xr nvd 4 driver is used to provide a disk driver to the system by default. The .Xr nda 4 driver can also be used instead. The .Xr nvd 4 driver performs better with smaller transactions and few TRIM commands. It sends all commands directly to the drive immediately. The .Xr nda 4 driver performs better with larger transactions and also collapses TRIM commands giving better performance. It can queue commands to the drive; combine .Dv BIO_DELETE commands into a single trip; and use the CAM I/O scheduler to bias one type of operation over another. To select the .Xr nda 4 driver, set the following tunable value in .Xr loader.conf 5 : .Bd -literal -offset indent hw.nvme.verbose_cmd_dump=1 .Ed .Pp .Sh SYSCTL VARIABLES The following controller-level sysctls are currently implemented: .Bl -tag -width indent .It Va dev.nvme.0.num_cpus_per_ioq (R) Number of CPUs associated with each I/O queue pair. .It Va dev.nvme.0.int_coal_time (R/W) Interrupt coalescing timer period in microseconds. Set to 0 to disable. .It Va dev.nvme.0.int_coal_threshold (R/W) Interrupt coalescing threshold in number of command completions. Set to 0 to disable. .El .Pp The following queue pair-level sysctls are currently implemented. Admin queue sysctls take the format of dev.nvme.0.adminq and I/O queue sysctls take the format of dev.nvme.0.ioq0. .Bl -tag -width indent .It Va dev.nvme.0.ioq0.num_entries (R) Number of entries in this queue pair's command and completion queue. .It Va dev.nvme.0.ioq0.num_tr (R) Number of nvme_tracker structures currently allocated for this queue pair. .It Va dev.nvme.0.ioq0.num_prp_list (R) Number of nvme_prp_list structures currently allocated for this queue pair. .It Va dev.nvme.0.ioq0.sq_head (R) Current location of the submission queue head pointer as observed by the driver. The head pointer is incremented by the controller as it takes commands off of the submission queue. .It Va dev.nvme.0.ioq0.sq_tail (R) Current location of the submission queue tail pointer as observed by the driver. The driver increments the tail pointer after writing a command into the submission queue to signal that a new command is ready to be processed. .It Va dev.nvme.0.ioq0.cq_head (R) Current location of the completion queue head pointer as observed by the driver. The driver increments the head pointer after finishing with a completion entry that was posted by the controller. .It Va dev.nvme.0.ioq0.num_cmds (R) Number of commands that have been submitted on this queue pair. .It Va dev.nvme.0.ioq0.dump_debug (W) Writing 1 to this sysctl will dump the full contents of the submission and completion queues to the console. .El .Pp In addition to the typical pci attachment, the .Nm driver supports attaching to a .Xr ahci 4 device. Intel's Rapid Storage Technology (RST) hides the nvme device behind the AHCI device due to limitations in Windows. However, this effectively hides it from the .Fx kernel. To work around this limitation, .Fx detects that the AHCI device supports RST and when it is enabled. See .Xr ahci 4 for more details. .Sh SEE ALSO .Xr nda 4 , .Xr nvd 4 , .Xr pci 4 , .Xr nvmecontrol 8 , .Xr disk 9 .Sh HISTORY The .Nm driver first appeared in .Fx 9.2 . .Sh AUTHORS .An -nosplit The .Nm driver was developed by Intel and originally written by .An Jim Harris Aq Mt jimharris@FreeBSD.org , with contributions from .An Joe Golio at EMC. .Pp This man page was written by .An Jim Harris Aq Mt jimharris@FreeBSD.org .