2.0Ghz CPU not scaling beyond 1.2Ghz in Vista

[amn]

Can anybody confirm Core 2 Duo CPUs not scaling up to their advertised frequencies in Windows (or other OSes like Linux) WHEN RUNNING ON AC WITHOUT BATTERY?

My 2.0Ghz Core 2 Duo only scales up to 1.2Ghz.

The issue disappears when battery is inserted, with or without AC from there on.

Thinkpad T61 14" WXGA+, Windows Vista 32bit

This appears to be a BIOS bug, but so far has not been fixed.

[comptiger5000]

Nope. Done by design with the 65w AC adapter. Just in case it can't push enough power at full load, with no battery for backup. The 90w adapter should allow full speed.

[amn]

Thanks for reply.

What are your sources? Or are you merely speculating?

According to wattage output when AC powered AND with a 7-cell battery pack inserted in the back, whole machine does consume at most 22 watts of power, about 17-18 on average, least recorded being ~15.5. That is well within limits of the adapter. If the ceiling frequency cutoff I described was by design, than it is a very debatable decision by Thinkpad engineers. I hardly would ever need 90 Watts of power to run a 14" Thinkpad T61 with Integrated graphics, a single mobile hard drive and a slimline DVD multiburner.

Another point against your statement: Why would the machine then scale up to 2.0Ghz when a battery IS attached in addition to machine being plugged in? The adapter then has to not only power the machine but ADDITIONALLY charge the battery SIMULTANEOUSLY, hardly a benefit from spare power usage perspective, but by your logic suddenly there is enough juice to power up the CPU at full frequency. This is certainly not the case, if part of power is used to charge the battery, but I can confirm the CPU scales up to 2.0Ghz just fine with 65W adapter and battery charging simultaneously.

There seem to be numerous if not overwhelming amount of reports, not only for Thinkpads, but many other Core 2 Duo laptops, where there seems to be a BIOS issue. Many of the following are debugged using Linux, but I CAN CONFIRM the story is the same when cold-booting into Vista.

Links to content describing the same story:
http://webui.sourcelabs.com/kernel/issues/10110
http://www.nabble.com/lower-CPU-clock-w ... 19381.html
http://www.mail-archive.com/acpi-bugzil ... 17069.html
http://www.thinkwiki.org/wiki/Problem_w ... cy_scaling

There are more, if you search Google.

I am of course open to explanations, and I did ask the question here in hope of Thinkpad owners being somewhat more knowledgeable about the issue.

If someone with a T61 preferrably, and using a 90W adapter, could remove the battery pack, and see if the CPU scales to advertised frequency while plugged into AC power only, I would appreciate the shared experience.

[comptiger5000]

It is simply a standard thing across all models of Thinkpads. For example, if I was using a 65w adapter on my W500, while gaming, or otherwise taxing both the CPU and GPU, with the screen brightness on full, there is a risk of overdrawing the adapter. In that case, it would use the battery to make up the difference, if it is installed. The 90w adapter would handle that just fine, however.

Your machine, however, uses less power. The limitation is still there, of course. Under normal use, the 65w adapter provides enough power to run the laptop and charge the battery. However, under heavy use, on some models, it may not. That's why that scaling is implemented, as it's better than the machine overdrawing the power adapter.

Sorry for the lengthy explanation, but it's kind of complicated.

[amn]

Well, your explanation, although I am grateful for your effort, does not settle well with my common sense. I am contacting Lenovo about this, and will post their answer here, so this issue is settled and other people may find this thread useful.

No offence, mate.

[bill bolton]

Well, your explanation, although I am grateful for your effort, does not settle well with my common sense.

This issue has been done to death here already on a number of occasions. Use the search option and you can find all the "proof" you would ever need!

Cheers,

Bill B.

[amn]

The problem is gone in Ubuntu 8.10, whatever cause, and however they did it. The 2.0Ghz CPU goes all the way up if needed, only on 65 watts of AC power, no battery present. Windows Vista still caps at 1.2Ghz. Go figure.

This makes matters even more confused, as to what is the real reason, no matter how many times it has "been done to death here."

[Harryc]

If the problem is 'gone' in Ubuntu while running a 65W adapter, then I would submit that they've implemented power management incorrectly in Ubuntu and there is a risk of over drawing the adapter. In XP, Vista, or another OS that handles it correctly, it is not a 'problem'. It is intentionally designed. I had a Macbook Pro that did the same thing. I bet there are many, many laptops out there with the same power design by default. If this is a major concern to you, your best option is purchasing a 90W adapter.

[phr]

I can tell you for sure that I experienced the difference in Ubuntu 8.4 and bought a 90w adapter as a result. I have a Ubuntu launchpad bug in about Thinkpad power management that I'll try to find. Maybe they made some changes because of it.