This OID reports the actual, currently negotiated PCI Express link speed in megabits per second for this device function, returning 0 if it could not be determined or the device is not PCIe. An admin diagnosing a performance shortfall on a PCIe card compares this negotiated speed against the slot's or card's maximum rated speed to see if the link trained down to a slower rate than expected. For example, a card rated for 8000 Mb/s but reporting a negotiated link speed of 2500 Mb/s here would indicate the PCIe link trained down to a much slower Gen 1 rate, worth investigating.