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Found in [Package]
7.3.1
Issue ID
1211228
Regression
Yes
[XR][XR SDK][HDRP] Semaphore.WaitForSignal usage spikes when using XR
How to reproduce:
1. Create a new project using HDRP template
2. Install XR Management Plugin in Project Settings or enable XR in Player Settings
3. Create and open a new empty scene
4. Open Profiler window
5. Enter Play mode and wait
Expected result: "Semaphore.WaitForSignal" doesn't spike
Actual result: "Semaphore.WaitForSignal" spikes between 0 - 80% of all running time
Reproducible with: 2019.3.2f1 (7.3.1), 2019.3.10f1(7.3.1), 2020.1.0b6(8.0.1), 2020.2.0a7 (9.0.0-preview 13)
Not reproducible with: 2018.4.21f1(5.16.1), 2019.3.1f1 (7.2.1)
Could not test with: 2017.4.39f1 (No HDRP package)
Notes:
- Tested with Oculus Rift
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Resolution Note:
This is not a performance issue but just profiling data to indicate when the **CPU** is waiting. It is not a busy work, it's just waiting for **VSYNC**.
For **VR**, it has a different **VSYNC** in place to reduce latency as much as possible. If it misses a frame, then the **XR Display** will decide to make you wait a bit more so that the next frame can be as optimal as possible.