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Can someone explain the behavior of this mobile CPU concerning 'turbo' mode?

post #1 of 3
Thread Starter 
I was running Tomb Raider 2012 on a i7-2630QM and while the game isn't single-threaded entirely, it doesn't seem to use much more than "1,5" cores, if that makes sense. So if I force the CPU to try to go to turbo mode with ThrottleStop, task manager appears to show that the cpu is used at no more than 13 to 15% (out of 8 virtual cores).

But, the game without any forcing with ThrottleStop appears to allow the CPU to lower its frequency to levels as low as around 800Mhz and the CPU showing use of up to 40% while the FPS of the game does not drop!

What is going on? I thought task manager would show 40% only if more than 3 virtual cores are used to the max, are they? Or does it show 40% just because the frequency is lower but it still uses only 1 or 2 cores max?(I doubt it).
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In any case the FPS does not raise if I try to force it to go to turbo mode at all times so I guess that wouldn't help much.

The bottleneck does seem to be the GPU, but could CPU really have so little impact? Does it mean a much worse CPU with a better GPU would be a much better combo? (I find that very likely).

Though something that concerned me is that throttlestop doesn't actually keep the cpu at turbo speed but it seems to fluctuate to lower frequencies for 20% of the time on CPUz.
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post #2 of 3
When trying to understand your CPU, turn off the Task Manager and turn off CPU-Z. Neither app accurately tracks what your CPU is doing when the amount of Turbo Boost is rapidly changing. CPU-Z flip flops back and forth between the lowest speed and the turbo speed and ignores a lot of the multipliers in between. It is a CPU MHz validation tool so keeps things simple when a CPU is idle or partially loaded.

Many games are mostly single threaded. The C0% number in ThrottleStop is a very accurate measure of how much of your CPU is being utilized. On a hyper threaded quad core CPU, you have 8 virtual cores so a single threaded task is going to use up one-eighth (1/8) of your CPU. The C0% number will be around 12.5% to take care of that task plus an extra percent or two to maintain the Windows background tasks running on your computer. The C0% data makes it very easy to determine how threaded an application is. When the Task Manager is set to view all cores or all threads, it makes it difficult to understand the data when viewed this way. Here is what a constant 25% load looks like when it is spread out to 4 cores.

rqq7.png


On the non-Extreme CPUs like your Core i7-2630QM, you can not simply lock your CPU to the maximum multiplier. The amount of Turbo Boost is constantly varying thousands of times a second based on how many cores are in the active state and whether the CPU is under the Turbo TDP limit or not. ThrottleStop uses high performance timers that run at billions of cycles per second so it can precisely track what the CPU multiplier is really doing. Run ThrottleStop with the Log File option checked and you will have an accurate record of your CPU's performance. When there is a load on your CPU, the Log File is not going to show your CPU throttling down to 800 MHz unless your laptop has a throttling issue.

For a GPU limited game, you can turn off Turbo Boost or significantly reduce the speed of your CPU without taking a big hit to FPS. Hyper threaded Quad core processors are processing beasts. Too many games don't even come close to utilizing what they are capable of.

Why not upload a ThrottleStop Log File while gaming so we can see what your CPU is really doing.

http://www.pastebin.com/
Edited by unclewebb - 6/15/13 at 11:44am
post #3 of 3
Thread Starter 
Hrm. OK thanks. It appears that Tomb Raider is massively multiprocessing since almost all virtual cores go above 40% (i.e. a single real core almost maxes) for a lot of the time.

That, or they fool us or/and they're doing it inefficiently. I suspect shenanigans since it doesn't seem to drop FPS if it isn't at max frequency.
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