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GPU Profile Giving Me the Finger?

So, I'm testing out Vulkan rendering on Linux. Got a simple scene rendering a static cube with a constant color. I've turned off some rendering features, as I'm working to get it running as fast as possible. I've also changed the Vulkan swap chain to run in "Immediate" mode, for the same reason.

The GPU stat in 'stat unit' was showing me a gpu time of around 0.6-0.9ms. However, nVidia's Linux Graphics Debugger was showing me fps spikes of over 4000fps! Their support of Vulkan is pretty new, so I had a feeling there's a bug in the tool.

But I thought I'd give the UE4 profiler a go to see what I could see. This is what I got:

alt text

You can see the "StatUnit GPUTime" bouncing around in purple. However, in green you can see the actual GPU [TOTAL] stat has an odd pattern going on. Looks like it's spending about half it's time doing absolutely nothing. The other half, it's bouncing around and even spiking in a regular pattern (looks like it's giving me the finger :P). All of the GPU sub-stats all show 0ms, with the exception of Postprocessing, which switches between 0ms when the [TOTAL] stat is 0ms, and 0.21ms when the [TOTAL] stat is bouncing around.

I'm at a loss for what's going on.

Anyone seen this before? Know what's happening? Surely something is not being tracked or written out properly or something.

Product Version: UE 4.19
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asked Apr 25 '18 at 08:17 PM in Rendering

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PhilBax
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