NAME

     nvme — NVM Express core driver

SYNOPSIS

     To compile this driver into your kernel, place the following line in your kernel configuration file:

           device nvme

     Or, to load the driver as a module at boot, place the following line in loader.conf(5):

           nvme_load="YES"

     Most users will also want to enable nvd(4) or 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.

DESCRIPTION

     The nvme driver provides support for NVM Express (NVMe) controllers, such as:

     •   Hardware initialization

     •   Per-CPU IO queue pairs

     •   API for registering NVMe namespace consumers such as nvd(4) or nda(4)

     •   API for submitting NVM commands to namespaces

     •   Ioctls for controller and namespace configuration and management

     The nvme driver creates controller device nodes in the format /dev/nvmeX and namespace device nodes in the
     format /dev/nvmeXnsY.  Note that the NVM Express specification starts numbering namespaces at 1, not 0, and
     this driver follows that convention.

CONFIGURATION

     By default, nvme 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.

     To force a single I/O queue pair shared by all CPUs, set the following tunable value in loader.conf(5):

           hw.nvme.per_cpu_io_queues=0

     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 loader.conf(5):

           hw.nvme.min_cpus_per_ioq=X

     To force legacy interrupts for all nvme driver instances, set the following tunable value in
     loader.conf(5):

           hw.nvme.force_intx=1

     Note that use of INTx implies disabling of per-CPU I/O queue pairs.

     To control maximum amount of system RAM in bytes to use as Host Memory Buffer for capable devices, set the
     following tunable:

           hw.nvme.hmb_max

     The default value is 5% of physical memory size per device.

     The nvd(4) driver is used to provide a disk driver to the system by default.  The nda(4) driver can also be
     used instead.  The nvd(4) driver performs better with smaller transactions and few TRIM commands.  It sends
     all commands directly to the drive immediately.  The nda(4) driver performs better with larger transactions
     and also collapses TRIM commands giving better performance.  It can queue commands to the drive; combine
     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 nda(4) driver, set the following tunable value in loader.conf(5):

           hw.nvme.verbose_cmd_dump=1

SYSCTL VARIABLES

     The following controller-level sysctls are currently implemented:

     dev.nvme.0.num_cpus_per_ioq
             (R) Number of CPUs associated with each I/O queue pair.

     dev.nvme.0.int_coal_time
             (R/W) Interrupt coalescing timer period in microseconds.  Set to 0 to disable.

     dev.nvme.0.int_coal_threshold
             (R/W) Interrupt coalescing threshold in number of command completions.  Set to 0 to disable.

     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.

     dev.nvme.0.ioq0.num_entries
             (R) Number of entries in this queue pair's command and completion queue.

     dev.nvme.0.ioq0.num_tr
             (R) Number of nvme_tracker structures currently allocated for this queue pair.

     dev.nvme.0.ioq0.num_prp_list
             (R) Number of nvme_prp_list structures currently allocated for this queue pair.

     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.

     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.

     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.

     dev.nvme.0.ioq0.num_cmds
             (R) Number of commands that have been submitted on this queue pair.

     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.

     In addition to the typical pci attachment, the nvme driver supports attaching to a 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 FreeBSD kernel.  To work around this limitation, FreeBSD
     detects that the AHCI device supports RST and when it is enabled.  See ahci(4) for more details.

SEE ALSO

     nda(4), nvd(4), pci(4), nvmecontrol(8), disk(9)

HISTORY

     The nvme driver first appeared in FreeBSD 9.2.

AUTHORS

     The nvme driver was developed by Intel and originally written by Jim Harris <jimharris@FreeBSD.org>, with
     contributions from Joe Golio at EMC.

     This man page was written by Jim Harris <jimharris@FreeBSD.org>.