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InfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable. The InfiniBand architecture specification defines a connection between processor nodes and high performance I/O nodes such as storage devices.



Users of Mellanox hardware MSX6710, MSX8720, MSB7700, MSN2700, MSX1410, MSN2410, MSB7800, MSN2740, and MSN2100 need at least kernel 4.9.[1]

The following kernel options must be activated:

KERNEL Enable InfiniBand support (CONFIG_INFINIBAND)
Device Drivers  --->
   <*> InfiniBand support  --->
      <*> InfiniBand userspace MAD support
      <*> InfiniBand userspace access (verbs and CM)
      <M> Mellanox HCA support
      <M> QLogic PCIe HCA support
      <M> Ammasso 1100 HCA support
      <M> Mellanox ConnectX HCA support
      <M> NetEffect RNIC Driver
      <M> Emulex One Connect HCA support
      <M> IP-over-InfiniBand
         [*] IP-over-InfiniBand Connected Mode support
      <M>   InfiniBand SCSI RDMA Protocol
In this example everything is selected. Most likely the userspace API (first two options) and the HCA (host channel/control adapter) drivers are needed for system specific hardware. IP-over-InfiniBand or srp modules may also be needed if they are required features.


If built as modules some of them don't neccessary get loaded automatically. The following file is an example for systemd systems.

FILE /etc/modules-load.d/InfiniBand.confmodules-load.d InfiniBand modules
# Some neccessary modules for InfiniBand

# Next one if for certain Mellanox harware. Pick appropiate for your hardware.
# umad is recommended, not mandatory, unless you explicitly use programs that need libibumad.
# For RDMA. You propably want these three if you have InfiniBand hardware, unless using IP-over-IB only.

Also make sure the module loading systemd service is enabled:

root #systemctl enable systemd-modules-load.service

USE flags

USE flags for sys-fabric/ofed OpenIB system files

dapl Add support for DAPL abstraction layer local
diags Add dignostic tools for infiniband local
ibacm Add support for userspace pre-connection services local
mstflint Tools to burn Mellanox firmware local
opensm Add OpenSM - Subnet manager for infiniband local
perftest Add perftest utils local
qperf Add rdma tests local
rds Tools to manage rds sockets local
srp Suport for userspace part for srp initiator local


root #emerge --ask sys-fabric/ofed


IP over InfiniBand (IPoIB)

Users of InfiniBand can also use it to carry IP-networking packets, thus allowing it to replace ethernet in some cases. From at least kernel version 4.10 onwards users can compile IP-over-IB in-kernel (CONFIG_INFINIBAND_IPOIB). However if that's not the case and the support is compiled as kernel module it may be possible that the module isn't automatically loaded. The module is named ib_ipoib:

root #modprobe ib_ipoib

InfiniBand network interfaces are usually named as ib<number>:

user $ifconfig ib0
ib0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 2044
Infiniband hardware address can be incorrect! Please read BUGS section in ifconfig(8).
        infiniband 00:00:04:04:FE:80:00:00:00:00:00:00:00:00:00:00:00:00:00:00  txqueuelen 256  (InfiniBand)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Performance tuning

When using IP over InfiniBand ther performance is usually low by default. This is because the default mtu of each InfiniBand IP interface is set to a low value.


The most conveivent way is to chance mtu automatically when kernel adds the interface to the system. Before mtu can be changed the mode of the interface must be changed to 'connected' from 'datagram' Next example uses udev rules to accoplish that.

FILE /etc/udev/rules.d/2-InfiniBand.rulesudev rules for InfiniBand IP networking interfaces
# Rules to set InfiniBand device attributes.

# Change mode to connected and change mtu to maximum for best performance.
ACTION=="add", KERNEL=="ib[0-9]*", SUBSYSTEM=="net", ATTR{mode}="connected", ATTR{mtu}="65520"

It has been reported[2][3] that the rule above does not work. Users with this problem may use the following instead:

FILE /etc/udev/rules.d/2-InfiniBand.rulesudev rules for InfiniBand IP networking interfaces
# Rules to set InfiniBand device attributes.

# Change mode to connected and change mtu to maximum for best performance.
ACTION=="add", KERNEL=="ib[0-9]*", SUBSYSTEM=="net", RUN+="/bin/sh -c 'echo connected > /sys/class/net/%k/mode && echo 65520 > /sys/class/net/%k/mtu'"

Mode and mtu can also be changed manually in run time. Next commands assume the interface in question is named ib0.

root #echo connected > /sys/class/net/ib0/mode
root #echo 65520 > /sys/class/net/ib0/mtu

Performance testing

There are several ways to test InfiniBand performance. When IP-over-InfiniBand has been set up propely users can use normal network performance testing tools for IP networks like net-misc/iperf. Most users however may want to use sys-fabric/qperf since it has the capability of testing the RDMA performance too. For example NFS can utilize RDMA in conjuction with IP networking[4].


Start qperf in one of the nodes:
root #qperf
This node now acts as a server.

Run tests on any client that has connection to the node(s) that now runs qperf in server mode. The following example runs tcp, upd and some rdma performance tests and assumes the qperf server node has an ip adress of

root #qperf ud_lat ud_bw rc_rdma_read_bw rc_rdma_write_bw uc_rdma_write_bw tcp_bw tcp_lat udp_bw udp_lat
    latency  =  27.6 us
    send_bw  =  676 MB/sec
    recv_bw  =  660 MB/sec
    bw  =  855 MB/sec
    bw  =  738 MB/sec
    send_bw  =  768 MB/sec
    recv_bw  =  735 MB/sec
    bw  =  656 MB/sec
    latency  =  51.2 us
    send_bw  =  719 MB/sec
    recv_bw  =  626 MB/sec
    latency  =  49.2 us

After the needed tests are complete stop the server process(es) just by hitting Ctrl+c on the terminal where the server-side qperf runs.


USE flags for net-misc/iperf A TCP, UDP, and SCTP network bandwidth measurement tool

sctp Support for Stream Control Transmission Protocol global
static-libs Build static versions of dynamic libraries as well global

iperf3, like qperf, needs a listening side to be started before actual performance testing.

Simplest way to start a iperf server process is:
root #iperf3 -s
However to reduce the output of the statistics on the server side users may want to limit the interval of the status updates. Next example set the interval to 10 seconds from the 1 second default:
root #iperf3 -s -i 10
Or suppress all normal output so that only errors are displayed:
root #iperf3 -s > /dev/null

Next run the client side iperf3 - again assuming the server has an ip address of

root #iperf3 -c -n 256G -i 60
Connecting to host, port 5201
[  4] local port 37670 connected to port 5201
[ ID] Interval           Transfer     Bandwidth       Retr  Cwnd
[  4]   0.00-60.00  sec  40.2 GBytes  5.76 Gbits/sec    0   3.25 MBytes
[  4]  60.00-120.00 sec  40.2 GBytes  5.75 Gbits/sec    0   3.25 MBytes
[  4] 120.00-180.00 sec  40.2 GBytes  5.75 Gbits/sec    0   3.25 MBytes
[  4] 180.00-240.00 sec  40.2 GBytes  5.75 Gbits/sec    0   3.25 MBytes
[  4] 240.00-300.00 sec  40.2 GBytes  5.76 Gbits/sec    0   3.25 MBytes
[  4] 300.00-360.00 sec  40.2 GBytes  5.76 Gbits/sec    0   3.25 MBytes
[  4] 360.00-382.07 sec  14.8 GBytes  5.75 Gbits/sec    0   3.25 MBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-382.07 sec   256 GBytes  5.76 Gbits/sec    0             sender
[  4]   0.00-382.07 sec   256 GBytes  5.76 Gbits/sec                  receiver

iperf Done.

The command above really puts the IP connection to a stress test by transferring 256 gigabytes of data which took over six minutes on this example. Users who just want quickly to see the bandwidth may run the following:

root #iperf3 -c -n 25G -i 5
... which transfers 25 gigabytes with 5 second interval between statistic reporting.

Refer to the iperf3 --help for more:

user $iperf3 --help
Usage: iperf [-s|-c host] [options]
       iperf [-h|--help] [-v|--version]

Server or Client:
  -p, --port      #         server port to listen on/connect to
  -f, --format    [kmgKMG]  format to report: Kbits, Mbits, KBytes, MBytes
  -i, --interval  #         seconds between periodic bandwidth reports
  -F, --file name           xmit/recv the specified file
  -A, --affinity n/n,m      set CPU affinity
  -B, --bind      <host>    bind to a specific interface
  -V, --verbose             more detailed output
  -J, --json                output in JSON format
  --logfile f               send output to a log file
  --forceflush              force flushing output at every interval
  -d, --debug               emit debugging output
  -v, --version             show version information and quit
  -h, --help                show this message and quit
Server specific:
  -s, --server              run in server mode
  -D, --daemon              run the server as a daemon
  -I, --pidfile file        write PID file
  -1, --one-off             handle one client connection then exit
Client specific:
  -c, --client    <host>    run in client mode, connecting to <host>
  -u, --udp                 use UDP rather than TCP
  -b, --bandwidth #[KMG][/#] target bandwidth in bits/sec (0 for unlimited)
                            (default 1 Mbit/sec for UDP, unlimited for TCP)
                            (optional slash and packet count for burst mode)
  --fq-rate #[KMG]          enable fair-queuing based socket pacing in
                            bits/sec (Linux only)
  -t, --time      #         time in seconds to transmit for (default 10 secs)
  -n, --bytes     #[KMG]    number of bytes to transmit (instead of -t)
  -k, --blockcount #[KMG]   number of blocks (packets) to transmit (instead of -t or -n)
  -l, --len       #[KMG]    length of buffer to read or write
                            (default 128 KB for TCP, dynamic or 1 for UDP)
  --cport         <port>    bind to a specific client port (TCP and UDP, default: ephemeral port)
  -P, --parallel  #         number of parallel client streams to run
  -R, --reverse             run in reverse mode (server sends, client receives)
  -w, --window    #[KMG]    set window size / socket buffer size
  -C, --congestion <algo>   set TCP congestion control algorithm (Linux and FreeBSD only)
  -M, --set-mss   #         set TCP/SCTP maximum segment size (MTU - 40 bytes)
  -N, --no-delay            set TCP/SCTP no delay, disabling Nagle's Algorithm
  -4, --version4            only use IPv4
  -6, --version6            only use IPv6
  -S, --tos N               set the IP 'type of service'
  -L, --flowlabel N         set the IPv6 flow label (only supported on Linux)
  -Z, --zerocopy            use a 'zero copy' method of sending data
  -O, --omit N              omit the first n seconds
  -T, --title str           prefix every output line with this string
  --get-server-output       get results from server
  --udp-counters-64bit      use 64-bit counters in UDP test packets

[KMG] indicates options that support a K/M/G suffix for kilo-, mega-, or giga-

iperf3 homepage at:
Report bugs to:

After the needed tests are complete stop the server process(es) just by hitting Ctrl+c on the terminal where the server-side iperf3 runs.