User Manual

Features Overview and ConfigurationRev 2.3-1.0.1

Mellanox Technologies

3.1.5 Checksum Offload

MLNX_OFED supports the following Receive IP/L4 Checksum Offload modes:

• CHECKSUM_UNNECESSARY: By setting this mode the driver indicates to the Linux

Networking Stack that the hardware successfully validated the IP and L4 checksum so

the Linux Networking Stack does not need to deal with IP/L4 Checksum validation.

Checksum Unnecessary is passed to the OS when all of the following are true:

• Ethtool -k <DEV> shows rx-checksumming: on

• Received TCP/UDP packet and both IP checksum and L4 protocol checksum are correct.

• CHECKSUM_COMPLETE: When the checksum validation cannot be done or fails, the

driver still reports to the OS the calculated by hardware checksum value. This allows

accelerating checksum validation in Linux Networking Stack, since it does not have to

calculate the whole checksum including payload by itself.

Checksum Complete is passed to OS when all of the following are true:

• Ethtool -k <DEV> shows rx-checksumming: on

• Using ConnectX®-3, firmware version 2.31.7000 and up

• Received IpV4/IpV6 non TCP/UDP packet

• CHECKSUM_NONE: By setting this mode the driver indicates to the Linux Network-

ing Stack that the hardware failed to validate the IP or L4 checksum so the Linux Net-

working Stack must calculate and validate the IP/L4 Checksum.

Checksum None is passed to OS for all other cases.

3.1.6 RDMA over Converged Ethernet (RoCE)

Remote Direct Memory Access (RDMA) is the remote memory management capability that

allows server-to-server data movement directly between application memory without any CPU

involvement. RDMA over Converged Ethernet (RoCE) is a mechanism to provide this efficient

data transfer with very low latencies on lossless Ethernet networks. With advances in data center

convergence over reliable Ethernet, ConnectX® EN with RoCE uses the proven and efficient

RDMA transport to provide the platform for deploying RDMA technology in mainstream data

center application at 10GigE and 40GigE link-speed. ConnectX® EN with its hardware offload

support takes advantage of this efficient RDMA transport (InfiniBand) services over Ethernet to

deliver ultra-low latency for performance-critical and transaction intensive applications such as

financial, database, storage, and content delivery networks.

RoCE encapsulates IB transport in one of the following Ethernet packet

• RoCE MAC based - dedicated ether type (0x8195)

• RoCE IP based - IP and dedicate IP protocol (0xfe)

• RoCEv2 - UDP and dedicated UDP port (1021)

When working with RDMA applications over Ethernet link layer the following points should be

noted:

• The presence of a Subnet Manager (SM) is not required in the fabric. Thus, operations

that require communication with the SM are managed in a different way in RoCE. This

does not affect the API but only the actions such as joining multicast group, that need to

be taken when using the API