Question
“ We have an application that is transfers data from a PCIe card to system memory in real time (approx 1.6 GB/s). This is currently running on a X9DA7 motherboard without issue, but when we try running the same PCIe card with the same software on the X11DAC motherboard we are having an issue where the buffers on the PCIe card overflow before the data can be DMAd to system memory. From what we've been able to tell so far, it appears to be related to latencies on the PCIe bus or memory that is holding up the DMA long enough that those on board buffers fill up. We have tried many different BIOS options and OS optimizations, but none of them have resolved the issue so far.  Is this an issue you have seen before. Are there any tools we could use to help track down the issue? Any optimizations that we can apply that may resolve the issue? “

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Answer
Because it is a third party card, we can't guarantee it will work all the time but if you want try.  Here are the steps:

1) First, you need to find out is by using lspci output, is the card and the PCI-E root port of CPU negotiate in optimized speed or not?
Example:
# lspci -s b4:00.0 -vv |grep -E "LnkCap|LnkSta"
                LnkCap: Port #9, Speed 8GT/s, Width x8, ASPM L1, Exit Latency L1 <4us
                LnkSta: Speed 8GT/s (ok), Width x8 (ok)
                LnkCap2: Supported Link Speeds: 2.5-8GT/s, Crosslink+ Retimer- 2Retimers- DRS-
                LnkSta2: Current De-emphasis Level: -6dB, EqualizationComplete+ EqualizationPhase1+

2) If the PCIe device is not detected in lspci, go to BIOS to check the PCIe train / link. 
Go to Chipset Configuration -> North Bridge -> IIO Configuration -> CPU1 or CPU2 Configuration (depends on which PCI-E slot your card is plugged into).   
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