Ubuntu Wiki

ASPM PCIe Bug

As noted by Phoronix ASPM PCIe power saving has been problematic and a recent patch by Matthew Garrett has re-worked this to clear the ASPM state on all devices on a successful handoff of PCIe control to the OS.

We therefore are providing patched kernels carrying Matthew's fix for testing purposes only to see how well this works across a broad range of machines. Kernels can be found in:

• Ubuntu Oneiric 11.10 Kernels

• Ubuntu Precise 12.04 Kernels

For power measurement, we currently recommend using the older version of powertop 1.13 as this clearly displays the ACPI estimated power consumption. A .deb for this can be found here. We recommend running powertop as follows:

• Boot the machine, start powertop 1.13
• Wait until you get an ACPI estimated power consumption value.
• Gather 15 measurements (it is updated regularly).
• Discard the 5 results.
• Take average of the last 10 results.

Testing procedure:

• Ensure laptop is fully charged
• Unplug AC power
• Run powertop on an idle system and note power consumption
• Plug in AC power
• Install the new kernel containing the ASPM fix
• Ensure laptop is fully charged
• Unplug AC power
• Run powertop on an idle system and note power consumption
• Gather the BIOS version using: sudo dmidecode -t 0 | grep "Version:"
• Add results to the table below:

Notes: Power estimation using ACPI battery data is not strictly accurate. We may see variation in data. It may be worthwhile repeating the test several times so we can see statistical variations in the gathered data.