What is Link State Power Management under PCI Express in the Power Management Options List

Here is the low down on what the "OFF" function does.

Off simply means that the current will run regardless of what state the laptop is in. (depending on if your laptop is plugged in or not).

Example:

On battery: Off

(PCI Express will communicate even when using battery power)

Plugged in: Off

(PCI Express will communicate when plugged in as well)

If you want to save more power while on battery then change the setting to "moderate" or "maximum." While your laptop is plugged in you should just keep it to "off" since you won't be using any of the battery. I hope this helps.

What about the third option which is setting PCI Express Link State Power Management to off? Is there any good reason when running on AC power to use Link State Power Management? Can you (or anyone else) point to a clear explanation of what LSPM does and how it might effect overall system performance (as perceived by the end user) if in fact it effects overall system performance at all?

Hi lapabc

Here is the explanation.

PCI Express has "active-state" power management, which lowers power consumption when the bus is not active (that is, no data is being sent between components or peripherals). On a parallel interface such as PCI, no transitions occur on the interface until data needs to be sent.

In contrast, high-speed serial interfaces such as PCI Express require that the interface be active at all times so that the transmitter and receiver can maintain synchronization. This is accomplished by continuously sending idle characters when there is no data to send. The receiver decodes and discards the idle characters. This process consumes additional power, which impacts battery life on portable and handheld computers.

To address this issue, the PCI Express specification creates two low-power link states and the active-state power management (ASPM) protocol. When the PCI Express link goes idle, the link can transition to one of the two low-power states. These states save power when the link is idle, but require a recovery time to resynchronize the transmitter and receiver when data needs to be transmitted. The longer the recovery time (or latency), the lower the power usage. The most frequent implementation will be the low-power state with the shortest recovery time.

Regards

Here is the best answer i found ....

The Link State Power Management is a part of PCI Express Active State Power Management (ASPM). The link State of a PCIe Device is converted from L0 (on) to L1 (off) when the link is not transferring data. The hardware is automatically converted to L0 again when data is available to transfer across the link. 

There are basically 2 levels of power management in the PCI Express options. The difference between these 2 options are the power savings versus the Latency (Time to recover from the Sleep state).

• If you select Off, there is no power savings, and the current will run regardless of what state the laptop is in. (depending on if your laptop is plugged in or not).
  • On battery: Off = PCI Express will communicate even when using battery power.
  • Plugged in: Off = PCI Express will communicate when plugged in as well.
• If you select Moderate Power Savings, the power savings are less, but the time to recover from the Sleep state (latency) is muchshorter.
• If you select Maximum Power Savings, the power savings are greater, but the time to recover from the Sleep state (latency) is muchlonger.

Sometimes this mechanism cause a bit trouble during power transitions, specially during sleep. So it may be wanted to turn the Link State Power Management off, if necessary. 

https://www.sevenforums.com/tutorials/292971-pcie-link-state-power-management-turn-off-windows.html