ib_read_lat Command

Performs a read latency diagnostic. Issued on the Linux InfiniBand host.

Syntax

ib_read_lat [-p TCP_port][-d device][-i IB_port][-c RC|UC][-m mtu][-o num][-s size][-a][-t depth][-n iters][-C][-H][-U][-V][-e][-F][IP_address]

where:

• TCP_port is the TCP port.

• device is the InfiniBand device.

• IB_port is the InfiniBand port.

• mtu is the size of the MTU.

• num is the outstanding reads/atom.

• size is the size of the messages.

• depth is the size of the TX queue.

• iters is the number of message exchanges.

• IP_address is the IP address of the remote node host.

Description

This InfiniBand software command performs a latency diagnostic between two nodes in the InfiniBand fabric. The command is dependent upon the Internet Protocol, so the InfiniBand fabric must be configured with Internet Protocol over InfiniBand (IPoIB). The command is a client-server, in that a remote node is configured as a server, while a local node performs as a client.

The command is first run locally on the server. The command is then run again locally on the client, pointing to the IP address of the server. The diagnostic checks the latency of the data transfer from the server to the client. The connection uses the Reliable Datagram transport. Optionally, you can set the connection between the nodes to use Reliable Connection or Unreliable Connection transport.

Options

The following table describes the options to the ib_read_lat command and their purposes:

Example

The following example shows how to run a diagnostic between a local node client and a remote node server with the ib_read_lat command. First configure the remote node server:

# ib_read_lat
------------------------------------------------------------------
                         RDMA_Read Latency Test
Connection type : RC
     local address: LID 0x01 QPN 0x9a0406 PSN 0x434b46 RKey 0x3688003a VAddr 0x00000001bfe080
     remote address: LID 0x05 QPN 0x230406 PSN 0x99013d RKey 0x2af8043f VAddr 0x000000118a3080
Mtu : 1024
#

Then run the command on the local node client:

# ib_read_lat 192.168.200.100
------------------------------------------------------------------
                         RDMA_Read Latency Test
Connection type : RC
     local address: LID 0x05 QPN 0x230406 PSN 0x99013d RKey 0x2af8043f VAddr 0x000000118a3080
     remote address: LID 0x01 QPN 0x9a0406 PSN 0x434b46 RKey 0x3688003a VAddr 0x00000001bfe080
Mtu : 1024
------------------------------------------------------------------
 #bytes #iterations    t_min[usec]    t_max[usec]  t_typical[usec]
         2        1000           9.44          96.39             9.73
------------------------------------------------------------------
#

Related Information

• ib_read_bw Command

• ib_send_lat Command

• ib_write_lat Command