On the Elusive Benefits of Protocol Offload.
Piyush Shivam, Jeff Chase (Duke University)
Periodic order-of-magnitude jumps in Ethernet bandwidth regularly
reawaken interest in TCP/IP transport protocol offload. This time the
jump to 10-Gigabit Ethernet coincides with the emergence of new network
storage protocols (iSCSI and DAFS), and vendors are combining these
with offload NICs to position IP as a competitor to FibreChannel and
other SAN interconnects. But what benefits will offload show for
Several recent studies have presented conflicting data to argue that
offload either does or does not benefit applications. But the evidence
from empirical studies is often little better than anecdotal. The
principles that determine the results are not widely understood, except
for the first principle: Your Mileage May Vary.
This paper outlines fundamental performance properties of transport
offload and other techniques for low-overhead I/O in terms of four key
ratios that capture the CPU-intensity of the application and the
relative speeds of the host, NIC device, and network path. The study
also reflects the role of offload as an enabler for direct data
placement, which eliminates some communication overheads rather than
merely shifting them to the NIC. The analysis applies to Internet
services, streaming data, and other scenarios in which end-to-end
throughput is limited by network bandwidth or processing overhead
rather than latency.