SoftRDMA: Implementing iWARP over TCP kernel sockets
by F. D. Neeser,
B. Metzler,
and P. W. Frey
Remote direct memory access (RDMA) allows for the minimization of
CPU and memory bus loads associated with network I/O. The
Transmission Control Protocol/Internet Protocol (TCP/IP)-based
Internet Wide Area RDMA Protocol (iWARP) stack now makes
RDMA available for Ethernet local area networks and wide area
networks. As 10-Gb/s Ethernet becomes deployed in data centers and
Ethernet link speeds continue to increase faster than the memory bus
bandwidth, the capability of RDMA to eliminate all intrahost data
copy operations related to network I/O makes it attractive for
accelerating TCP/IP. Whereas RDMA network adapters offload
iWARP/TCP functionality to dedicated hardware, we have designed
an onloaded iWARP software implementation, called SoftRDMA,
which runs on the host CPU, closely integrated with Linux® TCP
kernel sockets. SoftRDMA offers asynchronous nonblocking
user-space I/O. It enables iWARP with conventional Ethernet
adapters, as well as in mixed iWARP hardware and software
environments, facilitating RDMA system integration. Furthermore,
SoftRDMA benefits client–server applications with asymmetric loads
and high aggregate throughput on the server. With iWARP
checksumming turned off, SoftRDMA delivers a throughput exceeding
5 Gb/s using a single CPU core. We suggest zero-copy transmission
in software and hardware acceleration for the iWARP framing
layer for even higher performance.
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