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To look at the memory bandwidth in AMD’s 4th Gen EPYC CPUs, we used the STREAM benchmark. STREAM is a synthetic benchmark that is designed to measure sustainable memory bandwidth (in MB/s) and a corresponding computation rate for four simple vector kernels. We ran the benchmark on all four vector kernels in our study, and they showed a similar trend. Of all the vector kernels, Triad is the most complex scenario.
The performance unit for each operation is measured in MB/s, indicating the amount of data moved between the CPU and memory per second during that specific operation. The following figures show the system aggregate memory bandwidth for various DIMM sizes, performance per watt, and performance per dollar for STREAM–Triad across PowerEdge R7615 and R7625 servers with 4th Gen AMD EPYC 9654 and 9654P processors:
Figure 6. System aggregate memory bandwidth trends with different DIMM configurations and memory capacity for 4th Gen AMD EPYC processor-based PowerEdge R7615 and R7625 servers with default BIOS settings
Figure 7. Performance per watt trends with different DIMM configurations and memory capacity for 4th Gen AMD EPYC processor-based PowerEdge R7615 and R7625 servers with default BIOS settings
Figure 8. Performance per dollar trends with different DIMM configurations and memory capacity for 4th Gen AMD EPYC processor-based PowerEdge R7615 and R7625 servers with default BIOS settings
As the results show, the performance in PowerEdge R7625 is up to 98 percent higher than the performance in PowerEdge R7615.
Looking further at the results, the 2-socket, 12-DIMMs-per-socket balanced configuration with 32 GB DIMMs provides the best performance and energy efficiency. The 12-DIMMs-per-socket balanced configuration of 16 GB DIMMs provides the best performance per dollar.
For memory-bandwidth-bound workloads, we recommend the PowerEdge R7625 with an AMD EPYC 9654 in a balanced 12-DIMM configuration. It offers up to 49 percent better performance than the 8-DIMMs-per-socket configuration with 32 GB DIMMs.