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) 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)
•
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.
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.
SEE ALSO
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 [AT] FreeBSD.org>, with contributions from Joe Golio at EMC.
This man page was written by Jim Harris <jimharris [AT] FreeBSD.org>.
BSD January 7, 2016 BSD