I have a dual Xeon board with Intel C602 chipset and two E5-2670 CPUs. The board comes with five PCIe 3.0 x16 slots and a PCIe 3.0 x4 slot; all of which are directly connected to the CPUs.
I added a PCIe 3.0 card to a x16 slot connected to the first CPU ("BSP") as well as another card to the x4 slot (also connected to BSP). In both cases I find the that they are downgraded to PCIe 2.0 speed.
# lspci -vvs 82:00.0 | egrep '(82:00|GT)' 82:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller SM981/PM981 (prog-if 02 [NVM Express]) LnkCap: Port #0, Speed 8GT/s, Width x4, ASPM L1, Exit Latency L1 <64us LnkSta: Speed 5GT/s (downgraded), Width x4 (ok) LnkCtl2: Target Link Speed: 5GT/s, EnterCompliance- SpeedDis- # lspci -vvs 02:00.1 | egrep '(02:00|GT)' 02:00.1 Ethernet controller: Intel Corporation Ethernet Controller 10G X550T (rev 01) LnkCap: Port #0, Speed 8GT/s, Width x4, ASPM L1, Exit Latency L1 <16us LnkSta: Speed 5GT/s (downgraded), Width x4 (ok)
How may I assess why the link speed was downgraded and possibly rectify the problem?