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UPI Utilization

UPI traffic exists because the CPUs are communicating tasks to each other, constantly working to keep up

with user requests. SNAP I/O relieves the UPI of additional overhead by supplying a direct path to both CPUs

that doesn’t require UPI traversing, therefore freeing up

UPI bandwidth. It should come as no surprise that SNAP

I/O UPI traffic loading utilization is as low as 7%, while

standard riser UPI traffic loading utilization is at 63%.

CPU Utilization

While iperf was running for latency/bandwidth testing,

the CPU utilization was monitored. As we can see in

Figure 8, the SNAP I/O and Non-SNAPI sender-

remote utilization are identical, so SNAP I/O did not

have any impact here. However, the receiver-remote

utilization underwent a significant improvement,

seeing the Non-SNAPI configuration reduce from 55%

use to 32% use when configured with SNAP I/O. This

is due to the even distribution of TCP streams

reducing the average cache miss count on both CPUs.

Who Will Benefit from SNAP I/O

Using SNAP I/O to improve latency is most useful when the total cost of ownership (TCO) is priority, while

maximum bandwidth and card-level redundancy are not. Customers using a 100GbE NIC that need more

than 50Gb/s per CPU, or require two-card redundancy, may consider using a two-card solution to achieve

the same latency. SNAP I/O should be used in environments where low latency is a priority and single-NIC

bandwidth is unlikely to be the bottleneck. Environments such as containers and databases will thrive with

SNAP I/O configured, whereas virtualization environments are not yet compatible with the SNAP I/O riser.

Conclusion

Dual-socket servers using a Non-SNAP I/O riser configuration may suffer from unbalanced I/O or a higher

TCO. Having data travel from the remote socket across the UPI channel to reach the NIC introduces

additional overhead that can degrade performance.

SNAP I/O solution provides an innovative riser that allows data to bypass the UPI channel, achieving a direct

connection to a single NIC for two CPUs. As seen throughout this tech note, using a direct connection will

deliver higher network bandwidth, lower latency, lower CPU utilization and lower UPI traffic. Additionally, the

SNAP I/O solution is more cost-effective than purchasing a second NIC, cable and switch port.

Figure 8: Bar graphs comparing CPU utilization of sender and

receiver remotes for non-SNAP I/O and SNAP I/O

configurations

Figure 7: Comparison of UPI traffic loading percentages