Any way to get the GPU bound time in milliseconds?

Development Platform & Builds XR Development
1

Hi,
I’m trying to write a script (C++ or Blueprint) which needs access to the GPU bound time so I know exactly how long a frame took to process on the GPU.
I know you can use the delta on a frame tick - but this is similar to using Stat fps and it tells you the frame rate which locks to 90fps even if a frame only takes 5ms to render.
Does anyone know if there’s a way of finding out the render time of a frame in milliseconds?
Using the SteamVR>Settings>Performance>Display Frame timing shows the actual cpu/gpu bound time of each frame so it should be possible no?

Thanks

2 

     
/** How many cycles the renderthread used (excluding idle time). It's set once per frame in FViewport::Draw. */
extern RENDERCORE_API uint32 GRenderThreadTime;
/** How many cycles the gamethread used (excluding idle time). It's set once per frame in FViewport::Draw. */
extern RENDERCORE_API uint32 GGameThreadTime;
/** How many cycles it took to swap buffers to present the frame. */
extern RENDERCORE_API uint32 GSwapBufferTime;

const double CurrentTime = FApp::GetCurrentTime();
        const double DeltaTime = CurrentTime - FApp::GetLastTime();

        // Number of milliseconds in total last frame
        const double RawFrameTime = DeltaTime * 1000.0;

        // Number of milliseconds the gamethread was used last frame
        const double RawGameThreadTime = FPlatformTime::ToMilliseconds(GGameThreadTime);

        // Number of milliseconds the renderthread was used last frame
        const double RawRenderThreadTime = FPlatformTime::ToMilliseconds(GRenderThreadTime);

        // Number of milliseconds the GPU was busy last frame
        const uint32 GPUCycles = RHIGetGPUFrameCycles();
        const double RawGPUFrameTime = FPlatformTime::ToMilliseconds(GPUCycles);
3

Brilliant! That’s the stuff!
Cheers @mordentral :slight_smile:

4

Hey @mordentral (or anyone else that knows…)

The above code all works if I comment out the call to RHIGetGPUFrameCycles(); but adding that in does throw a linker error.
I have added the RenderCore module in the build.cs and have tried including DynamicRHI.h but it still throws the following if I try to compile with a call to RHIGetGPUFrameCycles();

The rest works though!

Any ideas what I’m missing that causes that lnk2001 ??

Thanks again

5

Found out it also needs the “RHI” module adding to the dependencies in the Build.cs.

6

Haha - me again!

So that code kinda works but as far as i can tell it actually just pulls the ‘rounded up’ frame time.

For example:
SteamVR is showing 6ms per frame on GPU and 3ms per frame on CPU.
The RawRenderThreadTime and RawGPUFrameTime from that script are both returning ~11ms - obivously rounding off to the 1/frame-rate with the frame-rate maintaining 90fps.

Any idea how I can pull the ‘6ms’ from within UE?

Thanks