Adds physics performance how-to guide (#2468)

# Description

Adds a new how-to guide on things to watch out for for better simulation
performance. There have been a few recent threads on hitting performance
issues due to usages of different collision geometries that can be
watched out for and worked around. This new doc page highlights items to
look out for to achieve better simulation performance.

## Type of change

- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

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docs/source/how-to/index.rst

@@ -134,3 +134,16 @@ teleoperation in Isaac Lab.
     :maxdepth: 1
 
     cloudxr_teleoperation
+
+
+Understanding Simulation Performance
+------------------------------------
+
+This guide provides tips on optimizing simulation performance for different simulation use cases.
+Additional resources are also linked to provide relevant performance guides for Isaac Sim and
+Omniverse Physics.
+
+.. toctree::
+    :maxdepth: 1
+
+    simulation_performance

docs/source/how-to/simulation_performance.rst

+Simulation Performance
+=======================
+
+The performance of the simulation can be affected by various factors, including the number of objects in the scene,
+the complexity of the physics simulation, and the hardware being used. Here are some tips to improve performance:
+
+1. **Use Headless Mode**: Running the simulation in headless mode can significantly improve performance, especially
+   when rendering is not required. You can enable headless mode by using the ``--headless`` flag when running the
+   simulator.
+2. **Avoid Unnecessary Collisions**: If possible, reduce the number of object overlaps to reduce overhead in the simulation.
+   Excessive contacts and collisions in the simulation can be expensive in the collision phase in the simulation.
+3. **Use Simplified Physics**: Consider using simplified physics collision geometries or lowering simulation fidelity
+   for better performance. This can be done by modifying the assets and adjusting the physics parameters in the simulation configuration.
+4. **Use CPU/GPU Simulation**: If your scene consists of just a few articulations or rigid bodies, consider using CPU simulation
+   for better performance. For larger scenes, using GPU simulation can significantly improve performance.
+
+Collision Geometries
+--------------------
+
+Collision geometries are used to define the shape of objects in the simulation for collision detection. Using
+simplified collision geometries can improve performance and reduce the complexity of the simulation.
+
+For example, if you have a complex mesh, you can create a simplified collision geometry that approximates the shape
+of the mesh. This can be done in Isaac Sim through the UI by modifying the collision mesh and approximation methods.
+
+Additionally, we can often remove collision geometries on areas of the robot that are not important for training.
+In the Anymal-C robot, we keep the collision geometries for the kneeds and feet, but remove the collision geometries
+on other parts of the legs to optimize for performance.
+
+Simpler collision geometries such as primitive shapes like spheres will also yield better performance than complex meshes.
+For example, an SDF mesh collider will be more expensive than a simple sphere.
+
+Note that cylinder and cone collision geometries have special support for smooth collisions with triangle meshes for
+better wheeled simulation behavior. This comes at a cost of performance and may not always be desired. To disable this feature,
+we can set the stage settings ``--/physics/collisionApproximateCylinders=true`` and ``--/physics/collisionApproximateCones=true``.
+
+Another item to watch out for in GPU RL workloads is warnings about GPU compatibility of ``Convex Hull`` approximated mesh collision geometry.
+If the input mesh has a high aspect ratio (e.g. a long thin shape), the convex hull approximation may be incompatible with GPU simulation,
+triggering a CPU fallback that can significantly impact performance.
+
+A CPU-fallback warning looks as follows: ``[Warning] [omni.physx.cooking.plugin] ConvexMeshCookingTask: failed to cook GPU-compatible mesh,
+collision detection will fall back to CPU. Collisions with particles and deformables will not work with this mesh.``.
+Suitable workarounds include switching to a bounding cube approximation, or using a static triangle mesh collider
+if the geometry is not part of a dynamic rigid body.
+
+Additional Performance Guides
+-----------------------------
+
+* `Isaac Sim Performance Optimization Handbook <https://docs.isaacsim.omniverse.nvidia.com/latest/reference_material/sim_performance_optimization_handbook.html>`_
+* `Omni Physics Simulation Performance Guide <https://docs.omniverse.nvidia.com/kit/docs/omni_physics/latest/dev_guide/guides/physics-performance.html>`_

source/isaaclab/docs/CHANGELOG.rst

@@ -13,7 +13,7 @@ Added
 
 
 0.38.0 (2025-04-01)
-~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~
 
 Added
 ~~~~~