I don't understand Unity Profiler Timeline view

Unity Engine
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Hi everyone,

I am working on a match 3 game and the match 3 section of the game runs very slowly on this old device that I have. It’s an Apple A7 chip device and the frame rate is around 15 fps. But even on a newer device (iPad 2019) this section runs around 45 to 50 fps compared to solid 60 in other sections.

The profiler Timeline view looks like this but I can’s understand what is happening here. Can you help me decipher it? It seems like the game is GPU bound, but the actual Gfx.PresentFrame time is around 3.83 ms.
The actual time is just spend on PrepareRenderTarget and I can’t find out what it is. And I also don’t understand why it seems that MainThread and RenderThread seem out of sync, the RenderThread stuff is kind of shifted to the right?!

8389956--1106997--upload_2022-8-25_16-42-40.png
8389956--1106997--upload_2022-8-25_16-42-40.png1920×962 124 KB

2

I think that in preparing the Render target the code is also waiting for a screen buffer to render too so, essentially it is also waiting for an earlier frame to be done with it’s screen buffer.
Are you using more render targets, e.g. for screenspace effects in this part of the gameplay? Otherwise I’d assume it is indeed GPU bound but maybe Frame debugger or XCode Instruments can provide more insights?