Adjust the fixed timestepA customizable frame-rate-independent interval that dictates when physics calculations and FixedUpdate() events are performed. More info
See in Glossary value to optimize physics simulation performance.
The physics system updates at a fixed time interval, which is important for accurate and consistent physics simulations. Configuring this frequency impacts the runtime performance of your project.
To review available project Time settings in the Editor, refer to Time.
Running multiple physics steps per frame can significantly affect performance. The fixed timestep value determines the interval at which the physics system updates its simulation. The default value of fixed timestep is 0.02, which corresponds to 50 fixed updates per second (50 Hz).
Game performance is negatively affected if multiple physics steps are required to keep pace with elapsed game time. For example, if game logic takes 35 ms to run in a frame and your Fixed Timestep value aims for 50 Hz (20 ms), the system might need to run two physics steps instead of one, which increases the computational load.
You can adjust the fixed timestep value to balance performance and simulation accuracy. However, consider the following trade-offs when adjusting the Fixed Timestep value:
To view or modify the Fixed Timestep setting:
On lower-end devices, or when the main thread is overloaded, a common performance issue occurs when the physics system runs multiple fixed updates per frame, leading to a cycle of increasing CPU load and frame time. This performance issue is often referred to as the “spiral of doom”.
If the physics system spends a long time processing a frame, it might run multiple fixed update steps within that frame to catch up with elapsed game time. Each additional physics step consumes more CPU resources, further increasing the total frame time. Longer frame times cause more physics steps, and this increased load then makes the next frame time even longer. This desynchronization and escalating CPU requirements can quickly waste calculations on outdated game states and severely degrade performance.
You can set a value for Maximum Allowed Timestep in the Time section of the Project SettingsA broad collection of settings which allow you to configure how Physics, Audio, Networking, Graphics, Input and many other areas of your project behave. More info
See in Glossary to limit the time spent on physics updates per frame if the main thread lags. However, this safeguard can cause the physics simulation to appear to slow down, so use it carefully.