Part of my focus this cycle is to see where we can make power saving improvements for Ubuntu Precise 12.04 LTS. There has been a lot of anecdotal evidence of specific machines or power saving features behaving poorly over the past few cycles. So, armed with a 6.5 digit precision multimeter from Fluke I've been measuring the power consumption on various laptops in different test scenarios to try and answer some outstanding questions:
* Is it safe to enable Matthew Garrett's PCIe ASPM fix?
* Are the power savings suggested by PowerTop useful and can we reliably enabled any of these in pm-utils?
* How accurate are the ACPI battery readings to estimate power consumption?
* Do the existing pm-utils power.d scripts still make sense?
* Which is better for power saving: i386, i386-pae or amd64?
* How much power does the laptop backlight really use?
* Does halving the mouse input rate really save that much more power?
* Should we re-enable Aggressive Link Power Management (ALPM)?
* Are there any misbehaving applications that are consuming too much power?
* What are the root causes of HDD wake-ups
* Which applications and daemons are creating unnecessary wake events?
* How much does the MSR_IA32_ENERGY_PERF_BIAS save us?
..and many more besides!
From some of the analysis and "crowd sourcing" tests it is clear that the PCIe ASPM fix works well, so we've already incorporated that into Precise.
Aggressive Link Power Management (ALPM) is a mechanism where a SATA AHCI controller can put the SATA link that connects to the disk into a very low power mode during periods of zero I/O activity and into an active power state when work needs to be done. Tests show that this can save around 0.5-1.5 Watts of power on a typical system. However, it has been known in the past to not work on some devices, so I've put a call for testing of ALPM out to the community so we can get a better understanding of the power savings vs reliability.
Some of the PowerTop analysis has shown we can save another 1-2 Watts of power by putting USB and PCI controllers of devices like Webcams, SD card controllers, Wireless, Ethernet and Bluetooth into a lower power state. Again, we would like to understand the range of power savings across a large set of hardware and to see how reliable this is, so another crowd sourced call for testing has been also set up.
So, if you want to contribute to the testing, please visit the above links and spend just a few tens of minutes to see we can extend the battery life of your laptop or netbook. And periodically visit https://wiki.ubuntu.com/Kernel/PowerManagement to see if there any new tests you can participate in.
I've written some brief notes on power saving tweaks and also some simple recommendations for application developers to follow too.
The thread continues here (part 2)