The Pull That Finally Fixes ASPM Power Regression for 3.3 (now 3.0.20 as well)

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Posted by Michael Larabel on January 11, 2012 (phoronix)

Queued up in the PCI sub-system pull for the Linux 3.3 kernel is the ASPM re-work that provides a proper fix to the well known Linux kernel power regression that was talked about for much of 2011.

This is still the nasty power regression in the Linux kernel that I discovered in early 2011 that was causing many systems (notebooks and desktops) to go through excessive amounts of power, which I then tracked back to being a change in the Active-State Power Management (ASPM) handling for PCI Express.

PCI-E ASPM was changed to what was believed at the time to be a more safe way of handling this power management feature, but it caused the power consumption to go up for many Linux systems. This led at least one vendor to just recommend using Windows, but ASPM (as with much of ACPI and power management) is a big grey area in Linux with guessing how to handle things due to varying vendor implementations and Microsoft not always enforcing / documenting well its standards.


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Posted by Michael Larabel on January 17, 2012 (phoronix)

Intel Has 50 Patches For ACPI/Power In Linux 3.3

The fun for the Linux 3.3 kernel merge window is not over quite yet; Intel this morning published 50 patches for integration into this next Linux kernel that affect ACPI and power management, primarily around ACPI 5.0 support for the Linux kernel.

The 50 patches for the 3.3 pull were submitted by Len Brown, the Intel OSTC developer who is also the ACPI sub-system maintainer for the Linux kernel. These new patches were largely authored by him and other Intel engineers, among others.

Among the notable changes in the ACPI pull is much work on ACPI 5.0, Turbostat support for Intel Ivy Bridge, a more robust Intel idle driver (especially for systems dealing with KVM virtualization), ACPICA (ACPI Component Architecture) updates, and APEI (ACPI Platform Error Interface) updates. From patch 20 for ACPICA, "this version contains full support for the ACPI 5.0 specification." There's also a fix that will allow some new motherboards (select P67/H67/Z68 motherboards) that can suspend but are not able to wake-up on Linux 3.2 and earlier, to now wake-up properly.


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Thank you for the update 

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Posted by Michael Larabel on February 06, 2012 (phoronix)

ASPM Linux Kernel Fix To Land Finally In 3.2 Series

The proper solution to the Linux kernel ASPM power regression will finally be landing in the stable Linux 3.2 kernel series.

The proper ASPM fix devised by Red Hat's Matthew Garrett late in 2011 went into the Linux 3.3 kernel, which is still currently under active development. The ASPM fix has since been patched into the kernels of another distro and Fedora, among other Linux distributions. his testing has undergone enough testing and review now that it looks like it's did the trick to fix the PCI Express Active State Power Management regression for many systems.

Greg Kroah-Hartman, now at the Linux Foundation, is preparing a special Linux 3.2 stable release that simply incorporates this PCI-E ASPM change. "It's a bit different from other stable review cycles in that it only has one patch. It's a fix to decrease power consumption on a wide range of different machines. I wanted to make this a separate release to make it easier for people to test it out in a simple way. This patch has been shipping in the Fedora kernels for a while now, so I'm pretty confident about it, but I'm doing it this way just to be sure. Please let me know if anyone has any problems with it as soon as possible."

This ASPM-kernel-release will be the Linux 3.2.5 version as mentioned on the kernel mailing list.

Phoronix

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H-Online / Heise - 7 February 2012

New Linux kernel fixes power-saving issues

Greg Kroah-Hartman has released long-term kernel 3.0.20 and stable kernel 3.2.5. Both contain just a single bug fix that allows PCIe power-saving technology ASPM (Active State Power Management) to be used on systems with a BIOS that activates ASPM on some components, but states in the FADT (Fixed ACPI Description Table) consulted by Linux that ASPM is not supported.

According to Matthew Garrett, who developed the patch, the change can reduce the power consumption of a Thinkpad X220 by 5 watts. The H's associates at c't magazine in Germany tested systems in their laboratory and experienced savings in the range of 1 to 3 watts which resulted in noticeably longer battery life. The patch only has this effect on systems with the firmware problem detailed above, which can be identified by using dmesg to display kernel messages and looking for the message "ACPI FADT declares the system doesn't support PCIe ASPM, so disable it".

The change fixes one of two problems which garnered serious attention last year as a result of reports on the Phoronix web site. Several weeks ago, the patch was merged into the main Linux development tree, which will form the basis of March's Linux 3.3 release. Patches like this, which could potentially cause problems on isolated systems, are not usually merged into long-term and stable kernels. The Fedora Project has, however, been testing the patch as part of its current distribution for some time, and Kroah-Hartman is therefore confident that the change will not cause any major problems. In view of the margin for error in this prediction, however, this is the only change in Linux 3.0.20 and 3.2.5.

Another problem which probably affects many more systems remains, however. By default, current Linux kernels do not activate the RC6 graphics power-saving feature on Intel's popular Sandy Bridge processors (which include a graphics core), as it has caused crashes and graphics errors on isolated systems. According to measurements made by c't, RC6 typically saves 3 to 5 watts when idling, which for laptops means reduced fan noise and longer battery life. It can be enabled for testing purposes using the kernel argument i915.i915_enable_rc6=1.

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