1.\" Copyright (c) 2016 The DragonFly Project. All rights reserved. 2.\" 3.\" This code is derived from software contributed to The DragonFly Project 4.\" by Matthew Dillon <dillon@backplane.com> 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in 14.\" the documentation and/or other materials provided with the 15.\" distribution. 16.\" 3. Neither the name of The DragonFly Project nor the names of its 17.\" contributors may be used to endorse or promote products derived 18.\" from this software without specific, prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 21.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 22.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 23.\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 24.\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 26.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 27.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 28.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 29.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 30.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31.\" SUCH DAMAGE. 32.\" 33.Dd June 5, 2015 34.Dt NVME 4 35.Os 36.Sh NAME 37.Nm nvme 38.Nd NVM Express Controller for PCIe-based SSDs 39.Sh SYNOPSIS 40To compile this driver into the kernel, 41place the following line in your 42kernel configuration file: 43.Bd -ragged -offset indent 44.Cd "device nvme" 45.Ed 46.Pp 47Alternatively, to load the driver as a 48module at boot time, place the following line in 49.Xr loader.conf 5 : 50.Bd -literal -offset indent 51nvme_load="YES" 52.Ed 53.Sh DESCRIPTION 54The 55.Nm 56driver provides support for PCIe storage controllers conforming to the 57NVM Express Controller Interface specification. 58NVMe controllers have a direct PCIe host interface to the controller 59which in turn has a direct connection to the underlying non-volatile 60(typically flash) storage, yielding a huge reduction in latency and 61increase in performance over 62.Xr ahci 4 . 63.Pp 64In addition, NVMe controllers are capable of supporting up to 65535 65independent submission and completion queues each able to support upwards 66of 16384 queue entries. Each queue may be assigned its own interrupt 67vector out of the controller's pool (up to 2048). 68.Pp 69Actual controllers typically implement lower limits. While most controllers 70allow a maximal number of queue entries, the total number of queues is often 71limited to far less than 65535. 8-32 queues are commonly supported. 72Similarly, while up to 2048 MSI-X vectors can be supported by the spec, 73actual controllers typically support fewer vectors. Still, having several 74MSI-X vectors allows interrupts to be distributed to multiple CPUs, 75reducing bottlenecks and improving performance. The multiple queues can 76be divvied up across available cpu cores by the driver, as well as split-up 77based on the type of I/O operation being performed (such as giving read 78and write I/O commands their own queues). This also significantly 79reduces bottlenecks and improves performance, particularly in mixed 80read-write environments. 81.Sh FORM FACTOR 82NVMe boards usually come in one of two flavors, either a tiny form-factor 83with a M.2 or NGFF connector, supplying 2 or 4 PCIe lanes, or in a larger 84form that slips into a normal PCIe slot. The larger form typically 85implements 2, 4, or 8 lanes. Also note that adapter cards that fit 86into normal PCIe slots and can mount the smaller M.2/NGFF NVME cards can 87be cheaply purchased. 88.Sh PERFORMANCE 89Typical performance for a 2-lane (x2) board is in the 700MB/s to 1.5 GByte/s 90range. 4-lane (x4) boards typically range from 1.0 GBytes/s to 2.5 GBytes/s. 91Full-blown PCIe cards run the whole gamut, 2.5 GBytes/sec is fairly typical 92but performance can exceed 5 GBytes/sec in a high-end card. 93.Pp 94Multi-threaded random-read performance can exceed 300,000 IOPS on an x4 board. 95Single-threaded performance is usually in the 40,000 to 100,000 IOPS range. 96Sequential submission/completion latencies are typically below 35uS while 97random submission/completion latencies are typically below 110uS. 98Performance (uncached) through a filesystem will be bottlenecked by additional 99factors, particularly if testing is only being done on a single file. 100.Pp 101The biggest differentiation between boards is usually write performance. 102Small boards with only a few flash chips have relatively low write 103performance, usually in the 150MByte/sec range. Higher-end boards will have 104significantly better write performance, potentially exceeding 1.0 GByte/sec. 105.Pp 106For reference, the SATA-III physical interface is limited to 600 MBytes/sec 107and the extra phy layer results in higher latencies, and AHCI controllers are 108limited to a single 32-entry queue. 109.Sh FEATURES 110The DragonFly 111.Nm 112driver automatically selects the best SMP-friendly and 113I/O-typing queue configuration possible based on what the controller 114supports. 115It uses a direct disk device API which bypasses CAM, so kernel code paths 116to read and write blocks are SMP-friendly and, depending on the queue 117configuration, potentially conflict-free. 118The driver is capable of submitting commands and processing responses on 119multiple queues simultaniously in a SMP environment. 120.Pp 121The driver pre-reserves DMA memory for all necessary descriptors, queue 122entries, and internal driver structures, and allows for a very generous 123number of queue entries (1024) for maximum performance. 124.Pp 125.Sh SEE ALSO 126.Xr intro 4 , 127.Xr pci 4 , 128.Xr ahci 4 , 129.Xr loader.conf 5 130.Sh HISTORY 131The 132.Nm 133driver first appeared in 134.Dx 4.5 . 135.Sh AUTHORS 136.An -nosplit 137The 138.Nm 139driver for DragonFly was written from scratch by 140.An Matthew Dillon Aq Mt dillon@backplane.com 141based on the NVM Expression 1.2a specification. 142