linux-kernel - Re: Possible bug in eeepc-laptop.c

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Date:	Wed, 10 Mar 2010 23:09:40 +0100
From:	Fabio Comolli <fabio.comolli@...il.com>
To:	Corentin Chary <corentin.chary@...il.com>,
	ACPI mailing list <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Len Brown <lenb@...nel.org>
Subject: Re: Possible bug in eeepc-laptop.c - EeePC 900

HI again.

On Wed, Mar 10, 2010 at 2:46 PM, Fabio Comolli <fabio.comolli@...il.com> wrote:
> Hi.
>
> On Wed, Mar 10, 2010 at 2:07 PM, Corentin Chary
> <corentin.chary@...il.com> wrote:
>> On Tue, Mar 9, 2010 at 11:58 PM, Fabio Comolli <fabio.comolli@...il.com> wrote:
>>> Hi.
>>> I have an EeePC 900 running 2.6.34-rc1.
>>>
>>> If I boot it on AC the cpu runs at full speed, 900MHz; if I boot it on
>>> battery it runs only at 630Mhz. Plugging / unplugging the AC does not
>>> change the cpu frequency. Only a reboot can change the situation.
>>>
>>> I already tried to echo 0 or 1 to the
>>> /sys/devices/platform/eeepc/cpufv file; no effects, even if the file
>>> changes its value.
>>>
>>> This is not a regression from 2.6.33: this behavior is also present in
>>> that version.
>>>
>>> Does this ring any bells? This is really annoying, especially when
>>> trying to watch a movie on battery. Also 3D apps show a 30%
>>> performance drop, as expected.
>>
>> Can you change the frequency with cpufreq ?
>
> No, I can't. Which cpufreq driver am I supposed to use? With only
> cpufreq compiled in, the directory
> /sys/drivers/system/cpu/cpu0/cpufreq is empty.

OK, there's something really wrong here.
I tried every possible cpufreq driver and the only one that loads is
p4-clockmod (the others say "no such device"). But...

The result is really unexpected, at least to me. The system switches
immediately to full speed, 900MHz (while running on battery). The
motivation is probably this:

[    3.698307] conservative governor failed, too long transition
latency of HW, fallback to performance governor
[    3.698334] p4-clockmod: P4/Xeon(TM) CPU On-Demand Clock Modulation available

The cause of this is probably that this driver thinks that my eeepc is
capable of many intermediate cpu frequency values:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
112500 225000 337500 450000 562500 675000 787500 900000

but the machine is only capable of 630 and 900MHz.

So, for me this is a really useful workaround: I compiled p4-clockmod
statically and so just a few seconds after boot I have my system
running at full speed :-)

To summarize:

-----Without p4-clockmod
* the eeepc-laptop cpufv interface doesn't work at all on my eeepc900
* this happens at least with 2.6.33 and 2.6.34-rc1
* if the system boots on AC power it stays forever at 900MHz
* if it boots on battery it stays forever at 630MHz

---With p4-clockmod
* the system boots at 630MHz if on battery
* as soon that p4-clockmod is loaded it switches to 900MHz
* p4-clockmod has a frequency table which is totally meaningless on the eeepc900

What a mess....

Regards,
Fabio

>
>> Did you try all cpufv values (see cpufv_available file) ?
>
> Yes, it only shows 0 and 1. I tried both, without success.
>
>> Is you bios up-to-date ?
>
> Yes it is, it's 1006.
>
>>
>> --
>> Corentin Chary
>> http://xf.iksaif.net
>>
>
> Thanks.
> Fabio
>
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