disabling a CPU increases laptop power consumption

Bug #54601 reported by Allison Karlitskaya
14
Affects Status Importance Assigned to Milestone
linux (Ubuntu)
Invalid
Undecided
Unassigned
linux-source-2.6.15 (Ubuntu)
Invalid
Low
Unassigned
linux-source-2.6.17 (Ubuntu)
Invalid
Low
Unassigned

Bug Description

Binary package hint: linux-source-2.6.15

This is a bit weird.

On my quest to improve battery performance on my laptop I learned about CPU hotplugging and how to take CPUs offline.

When I echo '0' to the online file for my CPU1 power use actually _increases_. I assume this to be caused by CPU1 running an (effective) busy loop once it goes offline but I am unable to confirm.

It would be nice if the CPU halted when taken offline. Disabling the second core of dualcore laptops would be a nice powersavings feature if it worked.

Revision history for this message
Allison Karlitskaya (desrt) wrote :

Bug is in edgy kernel too.

Matt Zimmerman (mdz)
Changed in linux-source-2.6.17:
importance: Untriaged → Low
status: Unconfirmed → Confirmed
Changed in linux-source-2.6.15:
importance: Untriaged → Low
status: Unconfirmed → Confirmed
Revision history for this message
Brian Murray (brian-murray) wrote :

I am assigning this bug to the 'ubuntu-kernel-team' per their bug policy. For future reference you can learn more about their bug policy at https://wiki.ubuntu.com/KernelTeamBugPolicies .

Changed in linux-source-2.6.17:
assignee: nobody → ubuntu-kernel-team
Changed in linux-source-2.6.15:
assignee: nobody → ubuntu-kernel-team
Revision history for this message
Sergio Zanchetta (primes2h) wrote :

The 18 month support period for Edgy Eft 6.10 has reached it's end of life. As a result, we are closing the linux-source-2.6.17 Edgy Eft kernel task. However, please note that this report will remain open against the actively developed kernel. Thank you for your continued support and help as we debug this issue.

Changed in linux-source-2.6.17:
status: Confirmed → Invalid
Revision history for this message
Sergio Zanchetta (primes2h) wrote :

Hardy Heron 8.04 was recently released. It would be helpful if you could test the new release and verify if this is still an issue - http://www.ubuntu.com/getubuntu/download . You should be able to test your bug using the LiveCD. Please let us know your results. Thanks.

Changed in linux:
status: New → Incomplete
Revision history for this message
Leann Ogasawara (leannogasawara) wrote :

The Ubuntu Kernel Team is planning to move to the 2.6.27 kernel for the upcoming Intrepid Ibex 8.10 release. As a result, the kernel team would appreciate it if you could please test this newer 2.6.27 Ubuntu kernel. There are one of two ways you should be able to test:

1) If you are comfortable installing packages on your own, the linux-image-2.6.27-* package is currently available for you to install and test.

--or--

2) The upcoming Alpha5 for Intrepid Ibex 8.10 will contain this newer 2.6.27 Ubuntu kernel. Alpha5 is set to be released Thursday Sept 4. Please watch http://www.ubuntu.com/testing for Alpha5 to be announced. You should then be able to test via a LiveCD.

Please let us know immediately if this newer 2.6.27 kernel resolves the bug reported here or if the issue remains. More importantly, please open a new bug report for each new bug/regression introduced by the 2.6.27 kernel and tag the bug report with 'linux-2.6.27'. Also, please specifically note if the issue does or does not appear in the 2.6.26 kernel. Thanks again, we really appreicate your help and feedback.

Revision history for this message
Jean-Baptiste Lallement (jibel) wrote :

Unfortunately this bug report is being closed because we received no response to the last inquiry for information. However, the Intrepid Ibex 8.10 Beta release was most recently announced - http://www.ubuntu.com/testing/intrepid/beta . If you are able to confirm this is still an issue with this most recent release please feel free to reopen this report. To reopen the bug report you can click on the current status, under the Status column, and change the Status back to "New".

Thanks,

Changed in linux:
status: Incomplete → Invalid
Revision history for this message
Launchpad Janitor (janitor) wrote : Kernel team bugs

Per a decision made by the Ubuntu Kernel Team, bugs will longer be assigned to the ubuntu-kernel-team in Launchpad as part of the bug triage process. The ubuntu-kernel-team is being unassigned from this bug report. Refer to https://wiki.ubuntu.com/KernelTeamBugPolicies for more information. Thanks.

Revision history for this message
Przemek K. (azrael) wrote :

Closing as per Jean-Baptiste comment.
Please reopen the linux task if you can reproduce this bug on Ubuntu 9.10 or 10.04.

Changed in linux-source-2.6.15 (Ubuntu):
status: Confirmed → Invalid
Revision history for this message
Stuart Hopkins (stuart-linux-depot) wrote :

Sorry to bring this one back alive, but i'm actually finding this problem still exists on Ubuntu 10.04 running the 2.6.32-24-generic-pae kernel.

I'm running a W510 laptop (quad-core) with HT disabled, and to try and save power (especially given the kernel interrupt problem atm) I tried disabling 1/2/3 of the 4 cores. My logic behind it was that the core would physically be powered down (no interrupts at all), and would use little to no power.

In doing this, powertop informed me my idle power usage rose from 17W to 33W, not good on a laptop! I can reproduce this each time by disabling a single or multiple cores. Also, if I re-enable them all, power usage decreases.

Given how this kernel interface is designed to allow for a CPU to be hotplugged in a live server, it seems strange in my mind that it is still supplying power to it.

Revision history for this message
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