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CPU: Intel Core 2 Duo P8400 @ 2.26GHz.

I've had this laptop for about 3 years and in the past month I've started getting periodic framerate drops in games. Usually the pattern is random, something like:

4 seconds of 29-31 ms/frame, 9 seconds of 66-68 ms/frame,
60 seconds of 29-31 ms/frame, 3 seconds of 66-68 ms/frame...

I've had this problem both in the game I'm developing (I'm a game programmer) and in OpenArena which I used to test this.

After some musing I think I've found the problem - the CPU is getting throttled, either to save power or to pervent overheating. Core Temp confirms this - it shows the CPU frequency fluctuating between 799MHz and 2260MHz and everything in between, and the low MHz periods coincide with framerate drops. This happens even when both cores have a temperature of 41 celsius, so I don't think it's due to overheating.

I looked for a setting to disable Intel SpeedStep in my BIOS, thinking I can go well enough without it, but there was no such setting in the BIOS (probably because of a custom OEM BIOS). I think this should be doable from my OS (win 7) too - I went to Control Panel -> Power Options -> High Performance -> Change plan settings -> Change advanced power settings -> Processor power management and set:

minimum processor state for plugged in = 100%
maximum processor state for plugged in = 100%
cooling policy for plugged in = Active

But there was no effect, even after a reboot.

Interestingly, there are long periods (many hours) in which the problem disappears and the CPU stays at a stable 2260MHz. Then it reappears. :)

So, it's not because of overheating, and it's not because of power saving (as I've told Windows that I'm not trying to save power). Any ideas?

Edit: the laptop is a Fujitsu Siemens Amilo Pi-3525

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How's the battery? If your battery is dying (even though running on mains) then you could have these symptoms. – Daniel R Hicks Mar 6 '12 at 13:25
Of course, another possibility is that the software doesn't run at a constant rate, due to housekeeping, etc. – Daniel R Hicks Mar 6 '12 at 13:27
Or you could have a stick of RAM that's running slow. – Daniel R Hicks Mar 6 '12 at 13:28
@Dan: the battery is good, got it replaced a few months ago. The problem is almost certainly not the software, as I've both debugged it thoroughly, and tested with another game. Would a bad stick of RAM explain the underclocking I see in Core Temp, do you know how I can check for this? – monov Mar 6 '12 at 14:03
I would have to investigate, using hard test. IntelBurn and furmark type of testing, see if I could force it to happen. With the disclaimer that those things come with. Watching the stepping, and the temps. An onboard temperature sencor for the chipset, and for the cpu, might not care at all about the "core temp" and certannly should care about the chipset(system) temps and the main cpu temps. So mabey read more temperature items? Plus you could read the voltages, but if that was the problem I think you would have different or more problems. – Psycogeek Mar 6 '12 at 17:03

If you've had this laptop for over 3 years, have you ever cleaned the dust off of whatever heatsink/fan/exhaust system it has? That would be the first place to look if you are overheating. Please add your brand and model and I can point you to a guide for getting the dust out.

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Thanks. I did take my laptop to a repair shop yesterday, they cleaned the dust and replaced the CPU thermal paste. That didn't help. But I'm not overheating anyway - I'm in the 40-60 celsius range. – monov Mar 6 '12 at 13:56

buy one of these instead.

no but srsly check to make sure you don't have anything in the background running as well (like an antivirus or something that might be doing scans) because background stuff may hamper your performance. If you don't have anything running that's visible, I'd say check in your task manager's process list and see what's spiking up when it starts happening.

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also how did that italics get in there I dont remember doing that. – SUPER MARIO BROTHERS Mar 6 '12 at 12:58
You used * characters around that word. It's part of the markup language used here. – Oliver Salzburg Mar 6 '12 at 13:23

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