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Thread: slow transfer speed on fermi cards

  1. #1
    Junior Member Regular Contributor
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    slow transfer speed on fermi cards

    I am getting very slow transfer speeds on the newest NVidia cards (GTX470/GTX480). glReadPixels() and texture upload speed is about 55% slower compared to previous generation cards (GTX280/GTX285).

    Tried different drivers, of course... same results.
    The hardware specs predict better results. (less bits memory address bus, but higher memory clocks)

    Can anyone report different results?

  2. #2
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    Re: slow transfer speed on fermi cards

    What platform?

  3. #3
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    Re: slow transfer speed on fermi cards

    Quote Originally Posted by randall
    What platform?
    Windows XP, drivers 197.x and 257.21.
    Tested on different mainboards, etc.

  4. #4
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    Re: slow transfer speed on fermi cards

    I got the same problem. With most Windows OS (XP - Seven 32 and 64 Bit)and NV drivers 197 and 257.

  5. #5
    Senior Member OpenGL Guru Dark Photon's Avatar
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    Re: slow transfer speed on fermi cards

    Quote Originally Posted by RDNXR
    I got the same problem. With most Windows OS (XP - Seven 32 and 64 Bit)and NV drivers 197 and 257.
    Are you seeing this on both your GTX 480 and QuadroFX 5800?

    We should post a short test prog for folks to run and compare readback rates between cards.

  6. #6
    Intern Contributor ruysch's Avatar
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    Re: slow transfer speed on fermi cards

    You guys have to come with something more solid than, "I got a 55% performance drop"; I aint saying its not true, but you aint giving any of us very much to work with.
    Knowledge is Power. Power Corrupts. Study Hard. Be Evil

  7. #7
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    Re: slow transfer speed on fermi cards

    Hello,

    I was able to build a small GLUT benchmark tool to show the differences in transfer speed on GTX480 cards.
    The app uses 720p HD resolution and RGBA Data.
    I added synchronous PBO transfers and surprisingly got very good result without using multiple buffers etc.
    The standard glReadPixels function seems to be the slow part on GTX470/GTX480...

    Some results:

    Geforce GTX480 driver 258.96
    ----------------------------
    glReadPixels: 8.10 ms
    PBO glReadPixels: 2.64 ms (memcpy 0.55 ms) total: 3.15 ms
    glTexSubImage2D: 1.25 ms
    PBO glTexSubImage2D: 0.02 ms (memcpy 0.56 ms) total: 0.58 ms
    glCopyTexSubImage2D: 0.04 ms

    Geforce GTX280 driver 197.45
    ----------------------------
    glReadPixels: 2.90 ms
    PBO glReadPixels: 2.60 ms (memcpy 1.17 ms) total: 3.77 ms
    glTexSubImage2D: 2.90 ms
    PBO glTexSubImage2D: 0.07 ms (memcpy 1.20 ms) total: 1.27 ms
    glCopyTexSubImage2D: 0.03 ms

    The two tests were run on different platforms hence the difference in memcpy speed. Will do a test with different cards on the same PC soon.

    Feel free to give the benchmark a try and post your results with GTX480. (I used maximum quality settings in the driver)

  8. #8
    Senior Member OpenGL Guru Dark Photon's Avatar
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    Re: slow transfer speed on fermi cards

    Quote Originally Posted by def
    transferBench.zip:
    -> transferBench.exe
    -> glut32.dll
    How about posting the source code too, so folks can run this exact same test on Linux with GTX480s and GTX285/280s.

    Thanks.

  9. #9
    Junior Member Regular Contributor
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    Re: slow transfer speed on fermi cards

    Here is a cleaned up version including source. Now using GLEW.
    Since I am using QueryPerformanceCounter() for timing calculations it's not completely portable yet.

  10. #10
    Member Regular Contributor trinitrotoluene's Avatar
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    Re: slow transfer speed on fermi cards

    For reference with a Radeon HD5870 on Linux here my result:
    Code :
    glReadPixels: 2.83 ms
    PBO glReadPixels: 1.08 ms (memcpy: 1.68 ms) total: 2.76 ms
    glTexSubImage2D: 1.23 ms
    PBO glTexSubImage2D: 0.05 ms (memcpy: 1.23 ms) total: 1.28 ms
    glCopyTexSubImage2D: 0.05 ms
    glGetTexImage: 2.72 ms
     
    memcpy speed: 2191 MBytes/sec
     
    Total frame: 16.87 ms  (total transfer: 9.65 ms)

    If people want the modified version of the source code to run on Linux I will post it.

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