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>.