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Something's underclocking my CPU

Last response: in Laptops & Notebooks
March 27, 2011 2:15:38 AM


Can someone please help me out here, I'm at my wits end! Noticed something weird about my NP5135 with i7 640m today and it's bugging the crap out of me.

The multiplier stays at x14 ~ 1.9ghz max when it should be x21 ~ 2.8ghz. I think it is software related but I have no idea what is actually causing the problem.

I have not done any over/under clocking on this laptop.

The reason I think it's software related is that the multiplier correctly goes up to x21 ~ 2.8ghz as soon as I enter desktop on boot up, but quickly gets limited to x14 ~1.9ghz when windows finishes loading everything. I have tried to terminate processes one by one while running prime95 to see which one is limiting it but had no success.

Here's some screenshots of processes running. If more info is needed please give me a shout.


i7 640m
4gig Ram
Windows 7 Home SP1
Geforce GT 425m

More about : underclocking cpu

a c 572 D Laptop
March 27, 2011 2:27:23 AM

Hello MizTEcK;

Does the 'underclocking' go away again when you start to run programs?
It's likely part of your power saving protocol. Slows down the CPU to save battery life when the laptop doesnt feel it needs full CPU

It's a 'feature' of your CPU called Intel Enhanced Speedstep Technology i7-640M CPU - look under 'Advanced Technologies'

Intel Core i7-640M CPU review
March 27, 2011 2:34:19 AM

Thanks for the reply. I know about the speedstepping, but the issue here is that even running prime95 on 100% max load the cpu only ramp up to x14 ~1.9ghz, when it should be running at 2.8ghz - 3.3 (on turbo) under full load.
Related resources
a c 572 D Laptop
March 27, 2011 2:49:08 AM

Check your power management options.
If you don't get better performance when you run on a high performance power management option it's time to talk to the MFGR.
March 27, 2011 2:53:51 AM

i'm on the high performance profile already with 100% processor power under max.

I don't think its a hardware issue because as I said there's a tiny window of time when I first enter desktop on boot that I can see the clockspeed working fine.

It's once windows finishes loading everything that this "limit" kicks in and maxes out the clockspeed at x14 on full load.
a c 572 D Laptop
March 27, 2011 2:54:33 AM

What are things like when you're running in Safe Mode?
March 27, 2011 2:59:08 AM

It is the limitation of the Turbo. If you stress all cores to the max, the multiplier will go up only 1x. That 2.7ghz turbo is when only 1 core is stressed while other cores are waiting for commands.
March 27, 2011 3:06:50 AM

HansVonOhain said:
It is the limitation of the Turbo. If you stress all cores to the max, the multiplier will go up only 1x. That 2.7ghz turbo is when only 1 core is stressed while other cores are waiting for commands.

Actually that's wrong, taken from Intel's spec sheet 2.8Ghz is the normal max, under turbo the i7-640m can actually go up to 3.46Ghz

Go into Device Manager, and uninstall Microsoft ACPI-Complaint System under System.
March 27, 2011 3:23:23 AM

Problem with Safe Mode is that CPU-Z will not detect the CPU, therefore I can't see the max clockspeed while running Prime95.

I uninstalled Mirosoft ACPI-Complaint System but that only uninstalled NVidia drivers and some controllers, which were instantly re-installed by windows 7 on reboot. Problem still exists
a c 572 D Laptop
March 27, 2011 3:45:26 AM

Resource Monitor / CPU tab will monitor "Maximum Frequency" in Safe Mode.
Run some other program than Prime95 as well.
March 27, 2011 3:54:27 AM

I'm in safemode right now and the resource monitor's frequency stats is obviously off because it shows 100% ALL THE TIME, even while idling with 0% CPU usage.

Any other ideas?
a c 572 D Laptop
March 27, 2011 4:06:20 AM

It could be correct if the SpeedStep isn't running.
Run Prime95 in normal and Safe Mode and compare the times.
March 27, 2011 5:23:38 AM

could it be that your just overheating really bad and the cpu is throttling itself down to maintain a safe temperature?
March 27, 2011 9:52:56 AM

Not sure but I believe the i7 can boost cores by sacrificing others - that is, it can make two cores act like a single, faster one. This is useful when software doesn't make use of more cores, but in the case of Prime95 this particular piece of software lends itself very well to multithreading, which makes it use all of your processor's cores, and as a result neither core can benefit from speed boost. Thus your overall speed per core doesn't exceed 1.9GHz. There's a simple test for this - try and set the affinity for Prime95 to only the first core - if the CPU goes up to 2.8+GHz, there's your answer.
March 27, 2011 4:51:55 PM

no his i7 is a dual core with ht and is rated at 2.8 ghz under normal conditions. it turbo boosts from there.
March 27, 2011 6:53:48 PM

the CPU's not overheating, maxes out at 60 degrees C and plus since it's only running on 1.9ghz on full load the fan doesn't even kick into maximum speed.
March 28, 2011 3:52:58 AM

What's the logithec KHAL process, and what does MacDrive do? Since the CPU seems to run normally at reboot, and then gets underclocked, it seems likely that there is a process that is scheduled to start with Windows that throttles the CPU at soon as it gets launched. User-defined power management settings would normally kick in at soon as a session is opened.

If you have a copy of XP lying around, or if you can download a Linux distro, a solution could be to try and dual-boot one of these OSes on the same hardware, and see if the CPU runs normally then. If it does, some software's messing with your i7.
March 28, 2011 12:55:07 PM

That's what I suspect as well. Logitech KHAL is the software that runs my mx518. MacDrive is a program that reads external harddrives that are formatted for MacOS.

I have removed MacDrive since the first post, didn't solve the problem. I think this is going to end up being a trial and error and even maybe result in a re-installation of win7 but it's near exam time I really don't have time for it.

I even restored my system to pre-SP1 installation and confirmed that SP1 upgrade did not result in this issue.