NVME(4) FreeBSD Kernel Interfaces Manual NVME(4)
NAME
nvme - Non-Volatile Memory Host Controller Interface
SYNOPSIS
nvme* at pci? dev ? function ?
DESCRIPTION
The nvme driver provides support for NVMe, or NVM Express, storage
controllers conforming to the Non-Volatile Memory Host Controller
Interface specification. Controllers complying to specification version
1.1 and 1.2 are known to work. Other versions should work too for normal
operation with the exception of some pass-through commands.
The driver supports the following features:
o controller and namespace configuration and management using
nvmectl(8)
o highly parallel I/O using per-CPU I/O queues
o PCI MSI/MSI-X attachment, and INTx for legacy systems
On systems supporting MSI/MSI-X, the nvme driver uses per-CPU IO queue
pairs for lockless and highly parallelized I/O. Interrupt handlers are
scheduled on distinct CPUs. The driver allocates as many interrupt
vectors as available, up to number of CPUs + 1. MSI supports up to 32
interrupt vectors within the system, MSI-X can have up to 2k. Each I/O
queue pair has a separate command circular buffer. The nvme
specification allows up to 64k commands per queue, the driver currently
allocates 1024 entries per queue, or controller maximum, whatever is
smaller. Command submissions are done always on the current CPU, the
command completion interrupt is handled on the CPU corresponding to the
I/O queue ID - first I/O queue on CPU0, second I/O queue on CPU1, etc.
Admin queue command completion is handled by CPU0 by default. To keep
lock contention to minimum, it is recommended to keep this assignment,
even though it is possible to reassign the interrupt handlers differently
using intrctl(8).
On systems without MSI, the driver uses a single HW interrupt handler for
both admin and standard I/O commands. Command submissions are done on
the current CPU, the command completion interrupt is handled on CPU0 by
default. This leads to some lock contention, especially on command ccbs.
The driver offloads command completion processing to soft interrupt, in
order to increase the total system I/O capacity and throughput.
FILES
/dev/nvme* nvme device special files used by nvmectl(8).
SEE ALSO
intro(4), ld(4), pci(4), intrctl(8), MAKEDEV(8), nvmectl(8)
NVM Express, Inc., NVM Express - scalable, efficient, and industry
standard, http://nvmexpress.org/, 2016-06-12.
NVM Express, Inc., NVM Express Revision 1.2.1,
http://www.nvmexpress.org/wp-content/uploads/NVM_Express_1_2_1_Gold_20160603.pdf,
2016-06-05.
HISTORY
The nvme driver first appeared in OpenBSD 6.0 and in NetBSD 8.0.
AUTHORS
The nvme driver was written by David Gwynne <
[email protected]> for OpenBSD
and ported to NetBSD by NONAKA Kimihiro <
[email protected]>. Jaromir
Dolecek <
[email protected]> contributed to making this driver MPSAFE.
NOTES
At least some Intel nvme adapter cards are known to require PCIe
Generation 3 slot. Such cards do not even probe when plugged into older
generation slot.
The driver was also tested and confirmed working fine for emulated nvme
devices under QEMU 2.8.0 and Oracle VirtualBox 5.1.20.
FreeBSD 14.1-RELEASE-p8 April 27, 2017 FreeBSD 14.1-RELEASE-p8