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I'm writing a linux app that talks from user space "directly" to a PCIe card, via DMA, without interrupts and kernel. My aim is to minimize the data travel time between the card and my app. Currently I'm getting latencies of about 800ns, while I was expecting about half that.

Questions: 1. Is there a way to configure PCIe latency? what are the parameters? 2. If not, are there motherboards with faster PCIe bus? I looked at few boards but didn't see PCIe latency numbers... what boards are good for that stuff?

Thanks!

BitWhistler
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    What kind of system do you have? On typical modern Intel-based systems, some of the PCI root ports are in the CPU chip. You should make sure you are using one of those instead of a port on the IOH (or whatever it’s called these days), by checking your mother board documentation. If you are, then the motherboard doesn’t matter, only the CPU chip does. – prl Mar 02 '20 at 04:32
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    By the way, DMA is when a device accesses memory. When the CPU accesses a device, that is not DMA; it is MMIO. – prl Mar 02 '20 at 04:34
  • Sorry for the late reply... I will check the mobo docs, but I believe it's connected properly. Thanks for the comment @prl. – BitWhistler May 02 '20 at 15:36

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