3.7. Active-State Power Management
Active-State Power Management (ASPM) saves power in the Peripheral Component Interconnect Express (PCI Express or PCIe) subsystem by setting a lower power state for PCIe links when the devices to which they connect are not in use. ASPM controls the power state at both ends of the link, and saves power in the link even when the device at the end of the link is in a fully powered-on state.
When ASPM is enabled, device latency increases because of the time required to transition the link between different power states. ASPM has three policies to determine power states:
- sets PCIe link power states according to the defaults specified by the firmware on the system (for example, BIOS). This is the default state for ASPM.
- sets ASPM to save power wherever possible, regardless of the cost to performance.
- disables ASPM to allow PCIe links to operate with maximum performance.
ASPM support can be enabled or disabled by the
pcie_aspmkernel parameter, where
pcie_aspm=offdisables ASPM and
pcie_aspm=forceenables ASPM, even on devices that do not support ASPM.
ASPM policies are set in
/sys/module/pcie_aspm/parameters/policy, but can be also specified at boot time with the
pcie_aspm.policykernel parameter, where, for example,
pcie_aspm.policy=performancewill set the ASPM performance policy.
pcie_aspm=forceis set, hardware that does not support ASPM can cause the system to stop responding. Before setting
pcie_aspm=force, ensure that all PCIe hardware on the system supports ASPM.