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Quadcore: slow clock speed due to multiple tasks?

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February 8, 2012 5:53:24 PM

Hello,


I've got an Intel Core i7 Q820 processor with four cores, clocked at 1.7 - 3.0 GHz. If I understand the architecture correctly, it uses full clock speed when there is only one demanding task, and when there are multiple tasks it clocks to a lower speed to save energy and warmth.
There seem to be particular slowdowns when I play a game and still have the browser open. Normally one would suppose that the demand of a browser in the background would be relatively small. However, could it be that simply by the four core architecture there is the problem that no matter how undemanding the background task itself, the tasks get separated to different cores and the clock speed remains far below the full potential. So that having a CPU like this results in much more significant slowdowns than having a CPU with less cores and more "stability" of clock speed.

That would also mean that the quadcore architecture has a significant weakness that somewhat defeats its purpose of higher efficiency (if it gets so easily and pointlessly slowed down).

More about : quadcore slow clock speed due multiple tasks

a c 154 à CPUs
February 8, 2012 5:57:05 PM

MatH said:
Hello,


I've got an Intel Core i7 Q820 processor with four cores, clocked at 1.7 - 3.0 GHz. If I understand the architecture correctly, it uses full clock speed when there is only one demanding task, and when there are multiple tasks it clocks to a lower speed to save energy and warmth.
There seem to be particular slowdowns when I play a game and still have the browser open. Normally one would suppose that the demand of a browser in the background would be relatively small. However, could it be that simply by the four core architecture there is the problem that no matter how undemanding the background task itself, the tasks get separated to different cores and the clock speed remains far below the full potential. So that having a CPU like this results in much more significant slowdowns than having a CPU with less cores and more "stability" of clock speed.

That would also mean that the quadcore architecture has a significant weakness that somewhat defeats its purpose of higher efficiency (if it gets so easily and pointlessly slowed down).


How much RAM do you have? Also it would help if you gave full system specs.
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February 8, 2012 6:05:05 PM

The system specs are without any particular bottleneck. I have 4GB RAM and a Radeon 5870 with 1GB.

I also haven't looked at any frame rate tool, but I notice slowdowns when I use a different screen with lower native resolution, whereas on a screen with higher resolution it seems to run smoothly all the time.

I might possibly be just imagining it, if you think the architecture shouldn't cause this kind of problem, but there seems to be a pattern.
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a b à CPUs
February 8, 2012 6:06:41 PM

OK...going out on a limb here...

You most lkely are talking about the Core i7 820QM. This is a mobile processor.

To reduce power signature and heat profile, the processor is designed to run at 1.73 Ghz stock. If it has a significant workload and it is plugged in, it will kick on the turbo boost and bump up the CPU ratio to gain an effective clock of 3.0 Ghz.

With a few adjustments to Windows, you can change you power usage profile and force the machine to run for performance. If you are running Windows 7, open up your control panel, go to Power Options and select the High Performance power plan. If you don't see it listed initially, click on the additional plans triangle and it will show up. What this means is that your laptop will now run full-bore no matter what the battery says. It also means your machine will run hot as well, so get a laptop cooler.

If you do operate in situations where you need to conserve battery power, go to the same control panel and either select Balanced or Power Saver.

Good luck.
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February 8, 2012 6:17:32 PM

You're correct, I copied the signature of the CPU from the hardware manager where it doesn't add an M for mobile. I use the laptop as a desktop replacement and use the high performance plan. So the turbo boost seems to be independent of minor background tasks, but it runs only for a measure of time and is rather unpredictable?
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a b à CPUs
February 8, 2012 6:22:20 PM

Your performance profile is telling the machine to be "sensible" about how it clocks the processor. If your performance profile is set to Power saver, for instance, it means that no matter what, those 4 cores are going to run at 1.73 Ghz.

That's why I said go into the Power Options control panel and turn it to High Performance. This won't be an issue if you have it plugged in at all times.

You can also (typically) force the clock to 3.0 Ghz in the BIOS. Not the best solution, but if you really want the performance, you can guarantee it this way.
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February 8, 2012 6:29:39 PM

That wouldn't be necessary, but there shouldn't be unpredictable slowdowns when more power is needed and available. Basically I just want to know if I can be sure it automatically uses the most performance available and doesn't randomly clock down.
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February 8, 2012 6:38:41 PM

4GB is so last decade. Laptop ? I would say slow disk and low on memory. Your CPU is fine. Most likely is idling 99% of time.

What type of stuff are you running simultaneously ?
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a b à CPUs
February 8, 2012 6:50:09 PM

Here's an idea. Pull the battery when you have it plugged into AC. Change your performance like I said and see what the processor decides to do.

You have 2 competing issues when you are dealing with laptops. First, battery power limits your processing power. By default, your OS (if it was installed by the integrator) will run the most efficient profile deemed possible by the engineer who designed the hardware. Second, as your processor does more and more work, it will generate more heat, and in some cases, more heat than it can reasonably dissipate. Hence, it will clock down performance regardless of the processing need just to keep the heat profile from getting out of hand.

Changing your power profile to performance and pulling the battery eliminates the power issue. Now, when you run processor-intensive tasks, you will need to monitor your CPU temperature and see if the machine turns down the clocks in response to high CPU temperatures. If this is the case, you need more active cooling (i.e., a laptop cooler) to help fight this issue.

Again, good luck.
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a c 186 à CPUs
February 8, 2012 7:19:06 PM

Top turbo boost is for single threaded tasks for example
i7-2600k
3.8ghz 1 core
3.7ghz 2 cores
3.6ghz 3 cores
3.5ghz 4 cores
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a c 85 à CPUs
February 8, 2012 7:33:30 PM

It works to a presumed thermal limit I think so it limits itself to a period of time at full pelt, and with a laptop that constraint is harsher than for a desktop.
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February 8, 2012 8:01:25 PM

Ok, I'll try to see how it reacts to heat.


radnor said:
4GB is so last decade.


It makes de facto no difference in 99% of cases. For example, it is of no relevance here.

radnor said:
Laptop ? I would say slow disk and low on memory. Your CPU is fine. Most likely is idling 99% of time.


"Slow disk", nice try. I can still differentiate between low framerate and loading problems. Yes, the CPU is indeed idling very much, but not so much when I'm playing a game.

In benchmarks that I've seen of the i5 and i7 CPUs there seems to be only a small difference in framerate (because the GPU is more important), but it would probably drop significantly below a certain threshold of clock speed when the GPU doesn't get sufficient support.


radnor said:

What type of stuff are you running simultaneously ?

A game (DX10-11 stuff, say, Mass Effect 2, normally very fast, except in some scenes), possibly Steam, and, as I said, a browser. Nothing special, basically just a game.


amuffin said:
Top turbo boost is for single threaded tasks for example
i7-2600k
3.8ghz 1 core
3.7ghz 2 cores
3.6ghz 3 cores
3.5ghz 4 cores


So, some automatic allocation of cores, when I've used the browser for a while and then start up a game, could cause slower performance?
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February 8, 2012 8:15:13 PM

OK, to be fair loading does make a difference in framerates. Some scenes are slow before they are fully loaded. But what I mean is an overall slower performance, or a drop in certain scenes that don't seem greatly demanding. It is hard to be completely sure, it's mostly a general impression, which is why I'm just asking for possibilities.
This is also an early i7, before the i5 were released (and it's used, but still good value).
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February 9, 2012 6:47:38 AM

MatH said:


It makes de facto no difference in 99% of cases. For example, it is of no relevance here.


A booted OS + Game + Background apps can take more than 4GB. Please shut off the pagefile and you will see it crash. One way to increase performance is to reduce the pagefile, so you can take the maximum benefit of your RAM.


MatH said:

"Slow disk", nice try. I can still differentiate between low framerate and loading problems. Yes, the CPU is indeed idling very much, but not so much when I'm playing a game.


Just download Process Explorer from sysinternals and check what is REALLY happening under the hood. Don't worry, it is virus free and it is mostly approved ny Microsoft.

MatH said:

In benchmarks that I've seen of the i5 and i7 CPUs there seems to be only a small difference in framerate (because the GPU is more important), but it would probably drop significantly below a certain threshold of clock speed when the GPU doesn't get sufficient support.


ME2 isn't too heavy on the hardware. Love that game and i'm waiting for the ME3 !

MatH said:

A game (DX10-11 stuff, say, Mass Effect 2, normally very fast, except in some scenes), possibly Steam, and, as I said, a browser. Nothing special, basically just a game.


ME2 is DX10, again check ProcessExplorer, see if you have any process using way more than expected.

MatH said:

So, some automatic allocation of cores, when I've used the browser for a while and then start up a game, could cause slower performance?


No, that would be ok. Again, you have a fine CPU that should take that load with a smile. use Resource Monitor and see "what" really is using all your resources. We are not talking about a Pentium 2 here. Last but not least, check to event viewer too see if some aplication of process is "borking" without notice.
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February 9, 2012 5:41:14 PM

Alright then, I used a tool to monitor the clock rate and heat. Even when the game is minimized, the clock rate remains fairly high (around 2.9 GHz). So there doesn't seem to be a depence on anything that goes on on the normal desktop. While the cooler gets fairly loud (as I already know), the temperature remains relatively steadyabout 89°. I think it would be clocked down at 100°. Also the performance in the Shogun 2 demo at Ultra is with or without desktop tasks equally bad in certains parts of high vegetation+shadow+units. So I guess the performance is overall on a steady rate (except perhaps after several hours).
Thanks for the answers, everyone.
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a c 85 à CPUs
February 9, 2012 6:42:19 PM

remember that the cpu and gpu share the same heat pipes, rad and fan.
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