Fw: ACPI and the idle loop - possible bug

Fw: ACPI and the idle loop - possible bug

[Andrew Morton]

Begin forwarded message:

Date: Sat, 25 Jun 2005 14:01:10 -0700
From: Stefan Baums <baums@u.washington.edu>
To: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: ACPI and the idle loop - possible bug


Some Lenove (IBM) ThinkPad models (in my case the ThinkPad X41
2528-6NU) produce irritating high-pitch crackling noises under
Linux in certain conditions, see the discussion here:

   http://thinkwiki.org/wiki/Problem_with_high_pitch_noises

This noise only occurs when the processor is not busy (with, e.g.,
compiling or video playback), so it seems to be related to the
idle loop (see also below about 'idle=halt').  Furthermore, it
seems to be caused by something that ACPI is doing to the
processor: if the 'processor' module (and its dependants:
'speedstep_centrino'/'acpi_cpufreq' and 'thermal') are not loaded,
the high-pitch noise does not occur.

If the 'processor' module (and its dependants) _are_ loaded, then
the noise can be initially avoided by passing the boot parameter

   idle=halt

to the kernel (causing it to halt, not poll, the processor during
idle loops), but this workaround _only_ works until either

   1) the system resumes from either suspend or hibernation, or

   2) the power state changes from battery to plugged-in or vice
      versa.

whereupon the high-pitch noise makes a return.

Taken all together, it would appear that the ACPI system is doubly
at fault:

   - First, for causing the high-pitch noise to start with, though
     it could be argued that this is a hardware defect that is
     just triggered by ACPI.  (However not by Windows XP, on the
     same computer, so it is definitely avoidable.)

   - Second, for apparently not respecting the kernel boot
     parameter "idle=halt" when it resumes or changes power state:
     it seems like ACPI is reverting to idle polling on those
     occasions.

Do you agree with this analysis?  Is it clear what ACPI's root
problem ('first' above) is, and will it be solved?  (Not loading
the 'processor', 'speedstep_centrino'/'acpi_cpufreq' and 'thermal'
modules - and losing their features - is not an acceptable
solution.)

As for the 'idle=halt' workaround: Is there any way to test
whether a running kernel actually uses polling or halt for the
idle loop?  What can I do to force ACPI never to use idle polling,
but halt instead?

My kernel version is Linux 2.6.12, custom-compiled on Ubuntu 5.04.
I have enabled all the usual ACPI features as modules.  The noise
problem occurs both with the 'speedstep_centrino' and the
'acpi_cpufreq' modules.  If necessary for diagnosis, I can put up
my kernel .config file online somewhere.

Many thanks for your help,
Stefan

PS.  Setting the polling frequency to 100 Hz instead of 1000 Hz at
compile time, as recommended by some people on the ThinkWiki page,
did not have any effect on the noise problem on my computer.

-- 
Stefan Baums
Asian Languages and Literature
University of Washington
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Re: Fw: ACPI and the idle loop - possible bug

[Janosch Machowinski]

> Some Lenove (IBM) ThinkPad models (in my case the ThinkPad X41
> 2528-6NU) produce irritating high-pitch crackling noises under
> Linux in certain conditions
This Problem also occures on a lot of ASUS Laptops,
sounds a bit like the morse alpabet ;-)

> This noise only occurs when the processor is not busy (with, e.g.,
> compiling or video playback), so it seems to be related to the
> idle loop (see also below about 'idle=halt').  Furthermore, it
> seems to be caused by something that ACPI is doing to the
> processor: if the 'processor' module (and its dependants:
> 'speedstep_centrino'/'acpi_cpufreq' and 'thermal') are not loaded,
> the high-pitch noise does not occur.
> 
My suggestion is that this sounds are created by the powerconverters.
And it only occurs on my ASUS M6 when the processor is in C3.
So the described behaviour is clear, cause if you unload the processor
ACPI module, you processor will stop going in C3 and thou the sounds
stop. 


> If the 'processor' module (and its dependants) _are_ loaded, then
> the noise can be initially avoided by passing the boot parameter
> 
>    idle=halt

What exactly does this parameter do ? Using for all C-States the hlt
instruction ?

>    - First, for causing the high-pitch noise to start with, though
>      it could be argued that this is a hardware defect that is
>      just triggered by ACPI.  (However not by Windows XP, on the
>      same computer, so it is definitely avoidable.)
> 
Could also be that XP dosen't use C3 as much as Linux does


	Janosch



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Re: Fw: ACPI and the idle loop - possible bug

[Stefan Baums]

> This Problem also occures on a lot of ASUS Laptops, sounds a bit
> like the morse alpabet ;-)

Yes, it does.  It is rather unpleasant.

> My suggestion is that this sounds are created by the
> powerconverters.  And it only occurs on my ASUS M6 when the
> processor is in C3.  So the described behaviour is clear, cause
> if you unload the processor ACPI module, you processor will stop
> going in C3 and thou the sounds stop.

   [...]

> >    idle=halt
> 
> What exactly does this parameter do ? Using for all C-States the
> hlt instruction ?

I have no idea.  A contributor to the ThinkWiki page that I
referred to had heard 'in several forums' that the problem may
have to do with the '"idle"-state (or "C3") of the processor'.
That got me googling, I came across the 'idle' kernel boot
parameter, and tried it out.  The documentation for this parameter
in linux-2.6.12/Documentation/kernel-parameters.txt is a
two-liner:

   idle=           [HW]
                   Format: idle=poll or idle=halt

and I could find no further information about this on the
Internet.  I guess somebody familiar with that part of the kernel
code will have to tell us what the parameter does.

Googling revealed that the C3 state seems to have caused another
(unrelated?) problem with the wireless driver on last year's
ThinkPad models:

   http://www.thinkwiki.org/wiki/Patch_disabling_ACPI_C3

That resulted in a patch to disable C3 (but not C2) entirely, but
I don't know if that patch still works with 2.6.12, and to be
honest, I'd rather keep my C3.  Whatever it is that idle=halt does
(until ACPI apparently switches it off) seems preferable.

Stefan

-- 
Stefan Baums
Asian Languages and Literature
University of Washington


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RE: Fw: ACPI and the idle loop - possible bug

[Li, Shaohua]

Hi,
>
>If the 'processor' module (and its dependants) _are_ loaded, then
>the noise can be initially avoided by passing the boot parameter
>
>   idle=halt
>
>to the kernel (causing it to halt, not poll, the processor during
>idle loops), but this workaround _only_ works until either
>
>   1) the system resumes from either suspend or hibernation, or
>
>   2) the power state changes from battery to plugged-in or vice
>      versa.
idle=halt will disable acpi idle, so it's not surprising it cures the
high noise issue. processor module has a parameter 'max_cstate', setting
it to 2 is a better workaround to me if you hate the noise.

Thanks,
Shaohua


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Re: Fw: ACPI and the idle loop - possible bug

[Stefan Baums]

> processor module has a parameter 'max_cstate', setting it to 2
> is a better workaround to me if you hate the noise.

Thank you very much for pointing out that option.  I am using it
now, and it is indeed a better workaround than idle=halt.

But it is a workaround.  On the one hand, it deprives me of C3 and
C4 and thus shortens my battery life.  On the other, I found it
exceedingly difficult to even find out about this option and get
it to work.  (I tried passing it to the module via
/etc/modprobe.d/ and /etc/modules, but neither one worked, and in
the end I had to compile the ACPI processor part directly into the
kernel and pass the option as a boot parameter
'processor.max_cstate=2'.)  But as you can see from the ThinkWiki
discussion, and Janosch’s post in this thread, there are indeed
quite a lot of users (of at least ThinkPads and Acer laptops) who
are affected by this problem and find the noise very unpleasant
and distracting.  As far as I remember, the noise was not there in
Windows XP on my machine (sorry, can’t check now, deleted
Windows), and as far as I know Windows XP does use the C3 state.
So do you think that you or the ACPI maintainers could try to
rewrite the Linux ACPI implementation so that it does not cause
this problem in C3?  I think it is not very good that on the
laptops concerned, a default Linux installation causes a constant
irritating noise and the only workaround (not solution) involves
finding the 'max_cstate' information, recompile the kernel (with
processor compiled in) and reconfigure the boot loader...  (In
case you do want to fix this and get a chance to test it out on a
ThinkPad X41: there the noise emerges from the ventilation vent on
the left-hand side of the laptop.  You may not hear it clearly in,
say, a noisy cafe or other public place, but it is very noticeable
in a quiet room.)

Finally, an unrelated problem is that ACPI apparently only honours
the idle=halt boot parameter until the first suspend/resume or
power state change, and then reenables C2 and above.

Do I need to file a separate formal bug report for these two
issues, and if so where?  Or is the discussion in this thread
sufficient for the ACPI maintainers to work with?

Best regards,
Stefan Baums

-- 
Stefan Baums
Asian Languages and Literature
University of Washington


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