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Multi GPU problem

artem909artem909 Posts: 0
in Technical Help (nuts n bolts)

Hi, guys! I have a problem. I connect 4 x 1080Ti, install latest drivers, they works fine.

In DAZ i select these 4 GPU (without CPU), but while rendering only 2 GPU working (1st and 2nd).

If i select only 3rd and 4th - they render fine.

Tried 4.11 and 4.12 beta, tried adding RAM - same results.

How to make work all of them? Please, help!

Comments

  • Richard HaseltineRichard Haseltine Posts: 102,669

    What operating system? What system specifications - system memory might, I think, be  cap.

  • kenshaw011267kenshaw011267 Posts: 3,805

    First, do you have SLI bridges installed? If so turn off SLI when rendering.

    Also how much RAM does your system have? Iray rendering does load up system RAM while rendering, particularly while loading the scene textures onto the cards.

  • artem909artem909 Posts: 0

    Windows 10 64bit, 16 Gb RAM.

    I have weak CPU - Celeron G4500 (3.5 GHz)... but this CPU is enough for crypto mining (all GPU works), so i dont think that CPU is the problem

  • artem909artem909 Posts: 0

    No SLI, 16 Gb RAM

    adding 8 Gb more - no changes  

  • kenshaw011267kenshaw011267 Posts: 3,805

    For 44Gb of VRAM you'll need a more RAM. I'd try at least 32 but you could easily need 64 or more.

  • artem909artem909 Posts: 0

    Some tests:

    4 Gb RAM - only 2 GPU rendering (system works slowly, but 4 Gb is enough)

    24 Gb RAM - only 2 GPU rendering.

    Tried my friends CPU intel i7 7700K with total 32 Gb RAM - still only 2 GPU rendering

    I dont know what to do crying

     

  • kenshaw011267kenshaw011267 Posts: 3,805

    Time to get down to the nitty gritty, what motherboard are you using? Did you verify that all the PCIE connections work? How are you sure only 2 GPU's are rendering?

  • RayDAntRayDAnt Posts: 1,147
    artem909 said:

    Windows 10 64bit, 16 Gb RAM.

    I have weak CPU - Celeron G4500 (3.5 GHz)... but this CPU is enough for crypto mining (all GPU works), so i dont think that CPU is the problem

    Iray dedicates 1 CPU thread per GPU for rendering in order to faciliate load balancing. From the official Iray documentation:

    4.11 Mixed mode rendering and load balancing

    Generally, Iray Photoreal uses all available CPU and GPU resources by default. Iray Photoreal employs a dynamic load balancing scheme that aims at making optimal use of a heterogeneous set of compute units. This includes balancing work to GPUs with different performance characteristics and control over the use of a display GPU.

    Iray Photoreal uses one CPU core per GPU to manage rendering on the GPU. When the CPU has been enabled for rendering, all remaining unused CPU cores are used for rendering on the CPU. Note that Iray Photoreal can only manage as many GPUs as there are CPU cores in the system. If the number of enabled GPU resourses exceeds the number of available CPU cores in a system Iray Photoreal will ignore the excess GPUs.

    The Celeron G4500 is a 2-core 2-thread CPU. Meaning that it is hard limited to supporting only 2 GPUs with Iray at any given time. 

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