Unstable File Recording Performance over NI MXI PCIe-8398 / PXIe-8398

Issue Details

I am trying to stream high-throughput data from a PXIe-1095 chassis to an external host workstation using the NI PCIe-8398- PXIe-8398. However, my sustained file recording performance to the workstation's local NVMe SSD fluctuates significantly and fails to hold a stable rate. 

What I am observing:

• My throughput frequently drops to 3.5 – 5.0 Gbit/s, failing to maintain the steady ~7.0 Gbit/s I need.

• I occasionally see performance peak at expected rates (6.5 – 8.0 Gbit/s), but I cannot consistently reproduce it.

• Interestingly, when I test this exact same configuration using an embedded PXI Controller and a PXIe SSD instead of the MXI link to the workstation, it streams perfectly and stably at 7 Gbit/s.

I found that Windows default or balanced power delivery profiles aggressively throttle PCIe link states, CPU C-states, and peripheral bus clocking. Even when standard BIOS-level power management features (like ASPM or C-States) are disabled, the operating system's underlying power sub-system can inject micro-latencies during sustained Direct Memory Access (DMA) block transfers over the external MXI bridge. This causes buffer fluctuations and drops my throughput.

Solution

To prevent Windows from throttling the bus and to stabilize my sustained recording throughput across the MXI-Express link, adjust the Windows power management scheme to its absolute highest performance state: 

1.Change the power plan from Power Saving to Best Performance/ Ultimate Performance

2. Turn OFF PCI Express Link State Management

Additional Information

Application Packet Size: Moving from a 16 KB packet size (which only gave me 2.0 to 4.0 Gbit/s) up to a 128 KB packet size significantly reduced CPU overhead and maximized my PCIe payload efficiency, bringing the throughput up into the 4.0 to 7.0 Gbit/s range. Ensure your application's DMA transfer size is optimized to at least 128 KB or higher.