we have a set of PCEs that are x4. When we configure this set of PCEs to be gen4 and use 4.0 PCEs with PCIE4.0*4 Samsung 990pro SSD, the test cannot achieve the speed of 4.0, read speed 4000m/s。
PCIe gen. 4 is16 GT/s. Keep in mind that the link speed is a raw speed. The theoretical max throughput also has to take into account the encoding. However, usually, if there is a correct mode, then there are other issues, e.g., if the transfer goes through the CPU and the CPU is under load, you won’t have an actual transfer as fast as the link. There are bottlenecks. DMA for example can improve things if it is a CPU bottleneck. Removing load of other software from that CPU can improve throughput.
Run “lspci” to find your device’s slot. I’ll pretend it is “00:00.0” (slot and device are different, not sure which your screenshot is showing). Then run this for your device and post the results: sudo lspci -s '00:00.0'
(this is the PCI driver telling you what it knows about the PCI settings for your specific device)
You might also want to describe how you are measuring actual speed other than viewing link speed. Run an app like “htop” (“sudo apt-get install htop”) and see if there is a particular core showing full load during that test.