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Multi-core usage

Discussion in 'General Software' started by Jonesi13, Mar 31, 2013.

  1. Jonesi13 New Member

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    Hello, I have an i7 920 with HT enabled and using Windows 7 x64 and I'm experiencing some issues with multi-core usage by applications.

    A lot of newer games and applications claim that they can utilize at least 2 cores for processing, yet almost all of my applications peak at 13% CPU usage, which indicates that they're only using one core. So far the only applications that have used more than 13% CPU have been CPU stress-testing applications, benchmarking applications and Skyrim (however only after I have explicitly written in the .ini files to use all cores; prior to that it was using only one core). Additionally used 3dsmax for a friend once and it also only used one core, despite selecting in the settings to use multiple cores.

    So, what am I missing here? Am I misreading the data? Do I have to do something extra to enable multicore-usage in general?
     
  2. Aquinus

    Aquinus Resident Wat-man

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    Welcome to TPU.

    I think I might have an answer for you.

    That's normal. My CPU does the same thing. We both have a 4c/8t CPU when hyper-threading is enabled. So one thread is "1/8 of your CPU power" (this isn't actually true, but the task manager treats it link this), which would equal out to about 12.5% of your "CPU power" once again under the false assumption that each thread is equal. In reality with how it is schedules though, it could be right, but I haven't seen proof of that.

    So generally speaking that's normal for a fully loaded single core. I bet you if you disabled hyper-threading it would look more like 25% which would be one of your cores as well.
     
  3. Dent1

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    How did you get to that conclusion. How do you know it's not using 6.5% of two cores or 3.25% of four cores?
     
  4. Jonesi13 New Member

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    Yes, if I disable HT i get a 25% peak.

    You are right on that part, the load is actually distributed more or less evenly on all 4 physical cores.

    However, why does the combined sum peak at the equivalent of one core?

    For example, in Skyrim if I don't edit the .ini the CPU load stays at 13% constantly. If I edit the .ini the load jumps to 20% average with peaks of up to 40% and with huge increases in game performance.

    So what exactly limits the applications to 12.5% (25% with HT off) CPU usage and what can I do to get past this?
     
  5. swellhunter New Member

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    Cores and threads, gross CPU load

    "However, why does the combined sum peak at the equivalent of one core?"

    This is very dependent on the sum of the "thread" activity. Currently few games balance the load over all cores. There may be one or two major threads only. Minecraft (clients) will happily hit 200% with 8 cores available. Speedstep helps flatten this too as multiplier changes affect all cores.

    If a core is not busy, then work is light *or* it is waiting for something. Hyperthreading becomes less effective with heavily CPU bound tasks. (prime number benchmarks and folding are good examples where HT is not going to work. It is common in these cases for piledriver minor cores to be disabled.)

    Your 8 cores are also diluting 500-800 Windows threads (not much CPU), new threads tend to be scheduled to fill the emptiest core, hence the appearance of balance. You could run task manager as the whole of a second screen (or behind your game) to watch this going on.

    If the CPU is "excessively waiting", it will be waiting for memory or GPU (which it should not be for graphics as this should be pretty asynchronous). There may be non graphic tasks running on the GPU too, but I doubt it ? The game has to run smoothly on lesser CPUs, or they won't sell as many copies right ?

    I have assumed you can see multiple cores in Task Manager, and that single core processing is not being enforced by BIOS.
     
    Last edited: Mar 31, 2013
    Dent1 says thanks.

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