Memory performance on HP Z840/Z640/Z440 Workstation

Channel 1 Channel 1
CPU0 CPU1
Channel 4 Channel 4
Channel 3 Channel 3
Channel 2 Channel 2
1 1
2 2
3 3
4 4
Figure 1. Memory channels
Note:
In a dual processor NUMA conguration (default for Z840/Z640), the interleaving of memory accesses among the channels is on a per
processor basis. With NUMA disabled, the interleaving of memory accesses among the channels would be across both processors.
Introduction
This paper looks at the performance impact of moving to larger DIMM sizes in
conjunction with populating fewer memory channels, for specic congurations
in HP Z840/Z640/Z440 Workstations.
As a general rule, memory performance is optimized when all memory channels
are populated in a system. Moving from a balanced memory conguration
(all memory channels populated) to an unbalanced memory conguration
(not all memory channels populated) will result in sub-optimal memory
performance. This performance impact will depend upon the application, workload
and the specic conguration being considered.
Memory performance in the HP Z840/Z640/Z440 Workstation
Each processor in the HP Z840, HP Z640 and HP Z440 Workstation supports four DDR4 memory channels. Each memory
channel provides a certain bandwidth capability, so by default the number of memory channels populated impacts
the achievable memory bandwidth in a system. In addition to providing the greatest memory bandwidth capability,
populating all memory channels (a balanced memory conguration) also allows the greatest interleaving of memory
accesses among the channels.
Technical white paper | Memory performance on HP Z840/Z640/Z440 Workstations
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