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I have an Intel Atom D510 based motherboard with a PCIe card connected to PCIe x4 connector on the motherboard. I am seeing very slow PCIe transfer speed with Centos 7.3, though with Ubuntu 16.04 I am seeing double speed which still is really slow compared to what I see on Intel Xeon based server. With Centos 7.3 and Ubuntu 16.04 look like they are using pcieport driver. Can I configure pcieport driver? What could be the reasons I am seeing slow transfer rate? Any help is appreciated.

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Atom D510 does not have onchip PCIe, it has x4 DMI that must be connected to a bridge chipset. As @mirh mentions, and confirmed in the diagram on page 6 of Intel's D510 reference schematic http://www.intel.com/content/dam/www/public/us/en/documents/schematic/dev-board-1-n450-d510-schematics.pdf, that's Gen1 so only 250 MB/sec (the schematic shows the ICH8M bridge chip).

On a Xeon based server, assuming at least PCIe Gen2, you might expect to see 2x speed.

Edit - also I found this Intel forum thread (https://embedded.communities.intel.com/thread/2464) where the OP seems to have done careful PCIe measurements using the ICH8M bridge chip, and he is reporting 2.5x slower reads than writes. If your tests are dependent on read performance, then this plus Gen1 gives you a 5x slow-down compared to a Xeon Gen2 server. That still doesn't account for the 10x slow-down you mentioned in your "Answer as a Comment" (in which you mentioned 10x slower for Ubuntu 16.04 and 20x slower than CentOS 7.3, both on a Gen2 Xeon server, and which I guess the moderators have unfortunately removed).

Also I might suggest changing your title to something like "Atom PCIe performance" since this is an Atom-specific discussion.

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  • @SignalStrength, what slow-down do you see compared to the Xeon server ? Is it like 2 or 3 times or like 10x slower ? Commented Feb 25, 2017 at 8:39
  • @SignalStrength, I see your "Answer as a Comment", I assume u didn't have the 50 pts (that's a problem with these forums). 10x or 20x speed is a dramatic difference, and implies issues beyond raw PCIe transfer rate. Maybe the bridge chip is not efficient, or doesn't have sufficient internal buffering. Although I don't know why latest CentOS would be any different than latest Ubuntu. Maybe due to kernel version Commented Feb 25, 2017 at 18:59
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PCH NM10 is PCIe 1.0 x4 only. I mean, like physically.

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