[ltp] Re: Applying undervolting patches

[David Abrahams]

Andrew Barr <andrew.james.barr@gmail.com> writes:

> On Tue, 2006-08-22 at 21:31 -0400, David Abrahams wrote:
>> Missing context: The following is from Scott J. Henson.
>
> Oops. Sorry.
>
>> Well, for me switching kernels has been nightmarish.  I'm surely
>> missing something very simple, but my wireless card has disappeared,
>> adn I can't seem to keep the proprietary ATI driver (8.28) working
>> under both the old and the new kernels.
>
> Hardware disappearing is because you don't have a driver for it. 

Something suddenly ripped the ipw3945 driver that comes with ubuntu
out of my stock kernel?

> You need to find out what the driver is that your wireless card uses
> and recompile it for the new kernel (or enable in the configuration
> it if it is in-tree).

Yeah, but why is it gone for the old kernel?

> I don't know about the ATI driver. Out of tree modules, proprietary or
> not, that use kernel APIs extensively (like device drivers) tend to
> break between kernel versions easily. Many times looking at communities
> (forums, mailing lists, wikis) that have a large number of users of a
> particular third-party module will have a patch to update them for new
> kernel versions.

At the moment I'm using the same kernel version with just a few minor
patches.  The question is why it stops working in one kernel when I
install it for the other kernel.  Don't they have separate modules
directories?

>> > It can be, depending on how low you can go with your
>> > undervolting. In my case, at 600 MHz (lowest frequency) I was able
>> > to go all the way down to 700 mV, which is the lowest you can go.
>> 
>> Are you talking about substantial gains due to undervolting, or due to
>> a kernel version upgrade?  Scott was suggesting that the kernel
>> version wouldn't make much impact.
>
> Well, I was originally talking about undervolting but from what I've
> heard both may have an impact. The 2.6.17 kernel has the best power
> management infrastructure of any released kernel to date.

That's my impression too.

>> BTW, how do you decide how low you can drive the voltages?
>
> Two steps: find how low you can go without locking up (there's a
> script to help you find this out at ThinkWiki), then download a
> computational test program (mprime95, also linked to at ThinkWiki)
> and see if your hardware is erring in computation of prime
> numbers. If it is, bump the voltages up a step (there is one voltage
> in a step of 16 mV for each available clock speed) and try
> again. Repeat this until you can run the test for a while (a few
> minutes is what I tried, it fails fairly readily if there's a
> problem IME) without errors.
>
> The particular procedure--including how to use mprime95 to test
> computation integrity--is at ThinkWiki. Gentoo-wiki.com also has a page
> about Pentium M undervolting which includes user-contributed voltage
> tables (incidentally, this is where I found a set that worked for me)

Seen that, but none for my CPU.  I took mine from NHC.  Although I
can't be 100% sure I know what those frequency scaling factors 6, 7,
...13 NHC uses are, I just assumed that 13 was 100% of the rated speed
and scaled down linearly from there.  NHC seems to have 8 steps while
linux-phc only seems to recognize 4.  Not sure what that means.

>> Well, they *were* tested against edgy according to the linux-phc
>> site.  But right now I'm conservatively using the dapper kernel with
>> patches.
>
> I can't imagine Ubuntu messes with the cpufreq drivers too much so they
> will probably apply to both vanilla trees and Ubuntu distro trees of
> supported versions.

linux-phc provides separate patches for vanilla and ubuntu sources.

>> > You might have better luck too using Debian linux-image and
>> > linux-source packages, even on Ubuntu, as they are very close to
>> > upstream.
>> 
>> Why would I have better luck with that?
>
> They are very close to kernel.org releases, but built using Debian
> kernel packaging tools. If you are having better luck with Ubuntu distro
> kernels, however, there's no reason to use Debian's packages.

It's hard to know how I'm having better luck, because trying any one
thing takes so long that I can't gather much data.

>> I have a vague memory that odd and even xx numbers have different
>> meanings (?)
>
> You're thinking of the 2.4 vs. 2.5 kernel series. 2.5 was an unstable
> development tree that eventually became the current 2.6 releases. There
> is no 2.7 for now (nor for the forseeable future due to change in the
> development model). The xx numbers have no odd/even significance.

OK, thanks.

>> So far my impression is that although there are ways to bend Linux to
>> your will if you have deep expertise, the system as a whole is
>> entirely too fragile.  Pull this lever over here, and something over
>> there breaks... :(
>
> Well, don't let that discourage you. :) It takes some time to get to
> know how to bend the system without breaking it. You learn a lot along
> the way. If you need a Windows partition to keep you productive while
> you spend your free time on Linux, so be it. 

Separate windows box at the moment.  The windows partition on my
Thinkpad stays, though.

> It's a great feeling to be able to finally save your personal files
> and delete that NTFS partition once and for all, but it does take
> time to get there.

Not gonna happen for me unless Wine becomes a thousand times better
than it is.  I have work I need to do with Windows.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com