Comment 87 for bug 760131

I did some digging on the lkml forums (hard to add links from the bby)

It looks like all of them relate to a series of commits for the kernel
IPI process. It looks to be added as a way to load balance processes
accross multiple cores in the fair scheduler (CFS) when the kernel is
running tickless (config_no_hz).

IPI is supposed to evaluate what core should handle the load balancing
process across all cores at any given time, based on which ones are
busy and idle. It looks to me to prefer keeping the load balance
process on a lightly loaded core so that the heavier processes don't
get impacted by the additional work of managing the other cores'
processes.

It sounds to me that it is a good way to keep high performance in a
server (especially as you increase the number of cores in the system,)
but I wonder if that may be the wong approach for a smaller system
looking to maximize power efficiency instead of raw performance.

On a single socket dual core system like atom, brazos, core2duo etc,
it doesn't seem to be necessary as the cores on a single socket share
cache and other resources.

I wonder if it would make more sense in the smaller systems (single
socket) to assign the load balancing process on one core, skip the IPI
altogether and only wake the other cores when there is work to do.
Perhaps even prefer to run new processes itself until it needs to wake
another core.

(Unfortunately, I am not a kernel hacker - If I am misunderstanding
any of this, I would welcome someone to correct me :)

On 6/10/11, Julian Kalinowski <email address hidden> wrote:
> This is getting OT, but how can you get 1141 wakups/sec when your top wakeup
> cause has only 33.7 wakeup/s ?
> I recently booted windows xp, which only consumes 8.5W compared to 12W in
> idle on ubuntu :(
> I'd really like the powersaving issue to be adressed..
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/760131
>
> Title:
> Power consumption raised significantly in natty
>
> Status in Release Notes for Ubuntu:
> Fix Released
> Status in “linux” package in Ubuntu:
> Triaged
> Status in “linux” source package in Natty:
> Incomplete
> Status in “linux” source package in Oneiric:
> Triaged
>
> Bug description:
> This is a regression moving from maverick->natty. With the same sort
> of light interactive usage, Battery life has gone from ~4 hours to
> 2:45 or so.
>
> Running powertop shows the system in P-state "Turbo mode" 10-15% of
> the time. Typically this was almost zero in maverick, 98+% of the
> time maverick was in the lowest state.
>
> wakeups reported in the 5-600/s range where previously (from memory)
> it was 200 ish. i915 driver is high on the list. This is
> irrespective of whether running unity or classic desktop.
>
> ProblemType: Bug
> DistroRelease: Ubuntu 11.04
> Package: linux-image-2.6.38-8-generic 2.6.38-8.42
> Regression: Yes
> Reproducible: Yes
> ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
> Uname: Linux 2.6.38-8-generic x86_64
> AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
> Architecture: amd64
> ArecordDevices:
>  **** List of CAPTURE Hardware Devices ****
>  card 0: Intel [HDA Intel], device 0: CONEXANT Analog [CONEXANT Analog]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> AudioDevicesInUse:
>  USER PID ACCESS COMMAND
>  /dev/snd/controlC0: james 2068 F.... pulseaudio
> CRDA: Error: [Errno 2] No such file or directory
> Card0.Amixer.info:
>  Card hw:0 'Intel'/'HDA Intel at 0xf2620000 irq 47'
>    Mixer name : 'Conexant CX20561 (Hermosa)'
>    Components : 'HDA:14f15051,17aa20ff,00100000'
>    Controls : 16
>    Simple ctrls : 8
> Card29.Amixer.info:
>  Card hw:29 'ThinkPadEC'/'ThinkPad Console Audio Control at EC reg 0x30,
> fw 7XHT24WW-1.06'
>    Mixer name : 'ThinkPad EC 7XHT24WW-1.06'
>    Components : ''
>    Controls : 1
>    Simple ctrls : 1
> Card29.Amixer.values:
>  Simple mixer control 'Console',0
>    Capabilities: pswitch pswitch-joined penum
>    Playback channels: Mono
>    Mono: Playback [on]
> Date: Wed Apr 13 15:03:35 2011
> EcryptfsInUse: Yes
> HibernationDevice: RESUME=UUID=bb479652-f524-4abe-b1b0-27646d6deebc
> InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release Candidate
> amd64 (20100928)
> MachineType: LENOVO 7465CTO
> ProcEnviron:
>  LANGUAGE=en_US:en_GB:en
>  PATH=(custom, user)
>  LANG=en_US.UTF-8
>  SHELL=/bin/bash
> ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.38-8-generic
> root=UUID=266abe9a-19c2-4cc3-9ef7-238b729b6044 ro quiet splash
> libata.force=noncq vt.handoff=7
> RelatedPackageVersions:
>  linux-restricted-modules-2.6.38-8-generic N/A
>  linux-backports-modules-2.6.38-8-generic N/A
>  linux-firmware 1.50
> RfKill:
>  0: phy0: Wireless LAN
>   Soft blocked: no
>   Hard blocked: no
> SourcePackage: linux
> UpgradeStatus: Upgraded to natty on 2011-04-06 (7 days ago)
> dmi.bios.date: 11/10/2009
> dmi.bios.vendor: LENOVO
> dmi.bios.version: 6DET61WW (3.11 )
> dmi.board.name: 7465CTO
> dmi.board.vendor: LENOVO
> dmi.board.version: Not Available
> dmi.chassis.asset.tag: No Asset Information
> dmi.chassis.type: 10
> dmi.chassis.vendor: LENOVO
> dmi.chassis.version: Not Available
> dmi.modalias:
> dmi:bvnLENOVO:bvr6DET61WW(3.11):bd11/10/2009:svnLENOVO:pn7465CTO:pvrThinkPadX200s:rvnLENOVO:rn7465CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
> dmi.product.name: 7465CTO
> dmi.product.version: ThinkPad X200s
> dmi.sys.vendor: LENOVO
>
> === Release Notes ===
>
> Due to a regression inherited from the upstream linux kernel, Natty 11.04
> can exhibit a 10-30% increase in power consumption. This is a known issue
> which is actively being investigated. A SRU will be released onced a viable
> solution is found. For more information, please see
>
> http://www.phoronix.com/scan.php?page=article&item=linux_mobile_uffda&num=1
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu-release-notes/+bug/760131/+subscriptions
>

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