Re:Server Hardware Super-Cycle 2022
by menaerus on Wednesday January 19, 2022 @09:47AM
(#29994224)
> DDR4 CAS latency is 15 clocks, which is about 9ns for highest clock frequency. Add to that cache latencies and memory controller latencies and you easily can get about 25-50 ns of latency and more.
On my 3rd gen Xeon E5 NUMA machine (two nodes) accessing adjacent memory bank is roughly around 90ns under no load. Accessing non-adjacent memory was around 120ns.
> 300ns is a latency of PCIe, not DRAM.
I'd figure that this number improved across different PCIe generations or? Have you got any tool to recommend that can measure this kind of thing? I found https://github.com/andre-richter/pcie-lat but haven't tried it yet.
On my 3rd gen Xeon E5 NUMA machine (two nodes) accessing adjacent memory bank is roughly around 90ns under no load. Accessing non-adjacent memory was around 120ns.
> 300ns is a latency of PCIe, not DRAM.
I'd figure that this number improved across different PCIe generations or? Have you got any tool to recommend that can measure this kind of thing? I found https://github.com/andre-richter/pcie-lat but haven't tried it yet.