Jetson Orin Developer Kit - unexpected drop in PCIe transfer speed

Hi, I am Burak. I am working on Jetson Orin Developer Kit which has Arm Cortex A78AE CPU. I am trying to take benchmark of PCIe transfer speed. But I encountered a strange situation. When I took benchmark of an PCIe Gen2 x4 port with Intel CPU, my graph is like attachment1(I

). The graph of PCIe Gen2 x8 port with Arm CPU on Jetson is like attachment2(



). I wonder why PCIe transfer speed of 2KB-4KB block sizes on Arm CPU is falling from 2GB/s to 200MB/s. Also, I couldn’t get near of theorical PCIe transfer speed, which is 4GB/s on PCIe Gen2 x8 port, but only half of it. I tried to debug this problem, and when I check “dmesg” command of Ubuntu OS, I saw many “arm-smmu: 12000000.iommu: Unhandled context fault: fsr=0x80000402, iova=0xffXXXXXX, fsynr=0x80013, cbfrsynra=0x1014, cb=6” messages. I can send all of this messages if you want.

I suspect that SMMU causes this transfer speed falling problem. Can you help me about that?