User Manual

Features Overview and ConfigurationRev 2.3-1.0.1

Mellanox Technologies

Step 2. Use rdma_cm test on the client.

# ucmatose -s 20.4.3.219

cmatose: starting client

cmatose: connecting

receiving data transfers

sending replies

data transfers complete

test complete

return status 0

This server-client run is without PCP or VLAN because the IP address used does not belong to a

VLAN interface. If you specify a VLAN IP address, then the traffic should go over VLAN.

3.1.6.3 Type Of Service (TOS)

The TOS field for rdma_cm sockets can be set using the rdma_set_option() API, just as it is set

for regular sockets. If a

TOS is not set, the default value (0) is used. Within the rdma_cm kernel

driver, the TOS field is converted into an SL field. The conversion formula is as follows:

• SL = TOS >> 5 (e.g., take the 3 most significant bits of the TOS field)

In the hardware driver, the SL field is converted into PCP by the following formula:

• PCP = SL & 7 (take the 3 least significant bits of the TOS field)

SL affects the PCP only when the traffic goes over tagged VLAN frames.

3.1.7 Explicit Congestion Notification (ECN)

ECN is an extension to the IP protocol. It allows reliable communication by notifying all ends of

communication when a congestion occurs.

This is done without dropping packets. Please note that since this feature requires all nodes in the

path (nodes, routers etc) between the communicating nodes to support ECN to ensure reliable

communication. ECN is marked as 2 bits in the traf

fic control IP header.

This ENC implementation refers to both RoCE and Routable RoCE.

ECN command interface is use to configure ECN activity. The access to it is through the file sys-

tem (mount of debugfs is required). The interface provides a set of changeable attributes, and

information regarding ECN's counters and statistics.

Enabling the ECN command interface is done by setting the

en_ecn module parameter of

mlx4_ib to 1:

options mlx4_ib en_ecn=1

3.1.7.1 Enabling ECN

 To enable ECN on the hosts

Step 1. Enable ECN in sysfs.

/proc/sys/net/ipv4/tcp_ecn = 1