MRDIMM 8800MT/s vs. DDR5-6400 Memory Performance With Intel Xeon 6

Last week when kicking off the Intel Granite Rapids benchmarking with the Xeon 6980P processors there was particularly strong performance within HPC and other scientific computing workloads. Besides going now up to 128 cores / 256 threads per socket, another reason for the especially strong generational uplift and against the current AMD EPYC competition is Xeon 6 Granite Rapids introducing Multiplexed Rank memory support. One of the areas I've been eager to explore is quantifying the DDR5-6400 vs. MRDIMM 8800MT/s performance difference and this article is dedicated to looking at that memory performance impact for the Xeon 6900P series.

The Intel Xeon 6900P series supports up to DDR5-6400MT/s memory or MRDIMMs up to 8800MT/s. Granite Rapids is the first platform supporting MRDIMMs for increasing the bandwidth even more than current DDR5 server memory. This article is looking at that DDR5-6400 versus MRDIMM-8800 performance difference on the dual Xeon 6980P server. Thanks to Intel for supplying the Granite Rapids reference server and both types of memory for making this review possible.

During the Granite Rapids briefing in Oregon, Intel talked up the DDR5-6400 memory performance as being up to 1.7x greater than Emerald Rapids when using DDR5-6400 memory or up to 2.3x greater than Emerald Rapids when using MRDIMMs.

Intel's marketing numbers quantified MRDIMMs as offering 1.32x the performance of DDR-6400 in the memory bandwidth intensive HPCG benchmark, 1.31x faster performance in the synthetic STREAM workload, up to 1.33x better performance in Llama-3, 1.2x the performance for OpenFOAM CFD, and more. Thus I was very eager to put Granite Rapids under my exhaustive benchmarking with both DDR5-6400 and MRDIMM 8800.

Intel supplied Micron 64GB 2RX4 PC5-8800X-HA0-1110-XT modules (PN: MTC40F2046S1HC88XDY WCCCC) as the MRDIMM 8800 modules during tesing while the DDR5-6400 DIMMs were the Micron 64GB 2RX4 PC5-6400B-RA1-1211-XT modules (PN: MTC40F2046S1RC64BDY QSFF). Twenty-four modules of each type for running all twelve memory channels with both sockets for this Intel Xeon 6980P testing.

So far I haven't seen any public pricing data to know what sort of premium MRDIMMs will initially command but presumably will be a hefty bit more than current DDR5 server modules.

This article is looking at the Xeon 6980P 2P performance both with DDR5-6400 and MRDIMM-8800 modules compared to a subset of the Intel Xeon and AMD EPYC CPUs used for last week's launch-day review. As a reminder all benchmarks were done on Ubuntu 24.04 LTS and each set of CPUs were running at their maximum number of memory channels and optimal supported frequency.

Let's see now the areas where MRDIMMs are worthwhile for significantly increasing server performance and the areas where there is less of an impact compared to conventional DDR5 server memory.