Re: Bug Report for Linux Kernel 3.x

[Frederic Weisbecker <fweisbec@gmail.com>]

(Please don't top-post)

On Tue, Aug 23, 2011 at 08:21:50PM -0400, Steevven1 wrote:
> QUICK NOTE - Thanks for replying directly to me as well as the mailing
> list. I am NOT on that mailing list. Please continue to do this.
> 
> That is correct about sparse irq. That was causing the first problem,
> and solving that did in fact result in better power performance, but
> it was apparently NOT the bulk of the problem.
> 
> We still have no diagnosis at all for the apparently still-present
> other (mystery) problem. Powertop now reports to me very low processor
> wakeups (basically the same as the 2.6-series kernels), which
> indicates to me that the problem is PROBABLY not related to processor
> wakeups. I am by no means an expert. The top wakeup-causers with the
> modified 3.0 kernel (no sparse irq) and an idle system are "[iwlagn]
> <interrupt>" (wifi), "[i915] <interrupt>" (I don't know what this is),
> and "[kernel scheduler] Load balancing tick"
> 
> P-states/frequencies are handled about the same as with the 2.6
> kernels, so I don't see a problem there either.
> 
> What else can I check? It seems like powertop is telling me nothing
> about this mystery power drain.

Well, if powertop has nothing to tell about that, I have no clue where
to go. I'm adding more people in Cc in the hope they can be more
helpful.

> 
> 
> On Tue, Aug 23, 2011 at 8:11 PM, Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > On Tue, Aug 23, 2011 at 07:19:35PM -0400, Steevven1 wrote:
> >> Hello,
> >>
> >> I would like to report what myself and several others believe to be a
> >> serious bug affecting all Linux kernels 3.0 and up, and none below 3.0
> >> (2.6.x and lower).
> >>
> >> One-sentence description: On certain hardware, the 3.x series kernels
> >> drain a considerable amount more power than the 2.6-series kernels, up
> >> to 40% more, even when idle.
> >>
> >> The specific hardware I have personally tested is a Lenovo ThinkPad
> >> X220 with an Intel SandyBridge i7 2620M processor. We think that this
> >> bug is POSSIBLY specific to this processor, or family of processors,
> >> commonly used in notebooks. A complete thread of mine and others'
> >> results, evidence, and troubleshooting process is located at:
> >> http://ubuntuforums.org/showthread.php?t=1822629
> >>
> >> We have tried several different 3.0 and 3.1-series kernels, all with
> >> the same problems. One part of the problem was that the following
> >> (revealed by powertop) was causing excessive processor wakeups
> >> compared to the 2.6-series kernels: "[Rescheduling interrupts] <kernel
> >> IPI>"
> >>
> >> Someone much more advanced than I figured out how to eliminate this
> >> problem and recompiled the kernel (which he posted in the thread I
> >> linked to previously), but power usage is still improved only
> >> slightly, nowhere near kernel 2.6 levels.
> >>
> >> There is a lot more information I could give you here, but all of it
> >> is contained within the thread I linked to. If you have any specific
> >> questions, I will answer as quickly as possible.
> >>
> >> Thanks a lot for your assistance. Please confirm that you received this email.
> >>
> >> Steven Keys!
> >
> > Hi Steve,
> >
> >
> > You said the problem with rescheduling interrupt disappeared but you
> > haven't said why. After reading the thread it seems it was about
> > Sparse irq config beeing enabled? And that disappeared after
> > sparse irq got disabled?
> >
> > If so that looks like a first bug.
> >
> > Also now that you don't see that problem anymore but still
> > a problem with power consumption, what does powertop report to
> > you?
> >
> > Thanks.
> >