Question Fps drops in very simple scene

Hi,
I am using Unity 2021.3 LTS with VR simple pass instanced and Open XR.
Randomly fps drops, i checked gpu usage in Unity and Windows and uses just about 70%, but still frames drop.
Most ms increase is cause Semaphone.WaitforSignal, which from what i read reflects that waits for another process which is making the delay, but dont know how to find that other process. I checked Timeline and found there is a Job worker using more than 100ms some times





Even if i just make an empty scene just with adding XR origin i get Semaphore.Waitforsignal and idle using ms

 

GPU bottlenecked for sure.
Did you disable SSAO?
Did you check the frame debugger?

 

Many thanks, it was SSAO, it is REALLY heavy, gpu uses usually less than 2ms without SSAO and with SSAO is about 9ms and also creates very intense lag spikes

 

I think you can reduce the costs of SSAO (depth + normals rendering) by setting the source to depth and enable after opaque (less accurate option).

 

After opaque is an optimization for mobile GPUs.
Depth is a bit faster, especially with lower normal quality.
For mobile also tick force prepass for the depth in the urp renderer