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SFM slows down to a crawl... with certain viewport layouts?

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  • SFM slows down to a crawl... with certain viewport layouts?

    I've tried to pin down the cause of this issue that has been encountered by a few filmmakers on varying hardware configurations. I'm on Windows 10 build 17134 (no "insider" stuff), with an Intel i7 4770, a GeForce 980 Ti with the 391.24 drivers (slightly behind, because recent nVidia releases have had some nasty bugs), 16GB of RAM, and two 1440p monitors.

    So here's what happens: we use the SFM as normal, we move stuff around, we manipulate lights, etc. and eventually the viewports will slow down immensely, to single-digit frame rates. It seems like sometimes we can get that problem to remedy itself by randomly screwing around with stuff, but we haven't found anything concrete, so I thought I'd try to investigate.

    I've tried to profile this issue with VPROF, and it might, hopefully, provide a programmer with interesting data. Both of these slices are 14-ish seconds.

    Slowdown not happening, for reference: (this was after restarting the engine, to be safe)

    Slowdown happening:

    I'm on a simple scene with viewport 1 showing the work camera, and viewport 2 being a light manipulator. Note the average of 8.5 fps.

    On the "slowdown not happening" VPROF, it's the same scene, but only one viewport. I'm doing the same thing in both cases: just wiggling the work camera around.

    The biggest observation that I can make is that CQViewportArea:: paintEvent goes from 33% to 76%, but most importantly from 4ms to 16ms in the "Avg-NoChild" measurement!

    I've also found that more the second viewport is resized (e.g. scaled down because you've put it in a tiny area of a column), the bigger the slowdown is.

    My hypothesis is therefore that this is a purely UI-related problem. I hope all this information helps.

  • #2
    It is with great shame that I will admit that I think I have found the real cause... the GeForce Experience (ugh) overlay.

    Which hooks into games and 3D apps even if you don't have any of its features enabled.

    Because that's a thing now apparently. (it wasn't always like this)

    (I'll let you know if it turns out to not be the cause though...)