Tricks and Troubleshooting#

Note

The following lists some of the common tricks and troubleshooting methods that we use in our common workflows. Please also check the troubleshooting page on Omniverse for more assistance.

Checking the internal logs from the simulator#

When running the simulator from a standalone script, it logs warnings and errors to the terminal. At the same time, it also logs internal messages to a file. These are useful for debugging and understanding the internal state of the simulator. Depending on your system, the log file can be found in the locations listed here.

To obtain the exact location of the log file, you need to check the first few lines of the terminal output when you run the standalone script. The log file location is printed at the start of the terminal output. For example:

[INFO] Using python from: /home/${USER}/git/orbit/_isaac_sim/python.sh
...
Passing the following args to the base kit application:  []
Loading user config located at: '.../data/Kit/Isaac-Sim/2023.1/user.config.json'
[Info] [carb] Logging to file: '.../logs/Kit/Isaac-Sim/2023.1/kit_20240328_183346.log'

In the above example, the log file is located at .../logs/Kit/Isaac-Sim/2023.1/kit_20240328_183346.log, ... is the path to the user’s log directory. The log file is named kit_20240328_183346.log

You can open this file to check the internal logs from the simulator. Also when reporting issues, please include this log file to help us debug the issue.

Using CPU Scaling Governor for performance#

By default on many systems, the CPU frequency governor is set to “powersave” mode, which sets the CPU to lowest static frequency. To increase the maximum performance, we recommend setting the CPU frequency governor to “performance” mode. For more details, please check the the link here.

Warning

We advice not to set the governor to “performance” mode on a system with poor cooling (such as laptops), since it may cause the system to overheat.

To view existing scaling_governor value per CPU:

cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

To change the governor to “performance” mode for each CPU:

echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

Observing long load times at the start of the simulation#

The first time you run the simulator, it will take a long time to load up. This is because the simulator is compiling shaders and loading assets. Subsequent runs should be faster to start up, but may still take some time.

Please note that once the Isaac Sim app loads, the environment creation time may scale linearly with the number of environments. Please expect a longer load time if running with thousands of environments or if each environment contains a larger number of assets. We are continually working on improving the time needed for this.

When an instance of Isaac Sim is already running, launching another Isaac Sim instance in a different process may appear to hang at startup for the first time. Please be patient and give it some time as the second process will take longer to start up due to slower shader compilation.

Receiving a “PhysX error” when running simulation on GPU#

When using the GPU pipeline, the buffers used for the physics simulation are allocated on the GPU only once at the start of the simulation. This means that they do not grow dynamically as the number of collisions or objects in the scene changes. If the number of collisions or objects in the scene exceeds the size of the buffers, the simulation will fail with an error such as the following:

PhysX error: the application need to increase the PxgDynamicsMemoryConfig::foundLostPairsCapacity
parameter to 3072, otherwise the simulation will miss interactions

In this case, you need to increase the size of the buffers passed to the SimulationContext class. The size of the buffers can be increased by setting the gpu_found_lost_pairs_capacity parameter in the PhysxCfg class. For example, to increase the size of the buffers to 4096, you can use the following code:

import omni.isaac.orbit.sim as sim_utils

sim_cfg = sim_utils.SimulationConfig()
sim_cfg.physx.gpu_found_lost_pairs_capacity = 4096
sim = SimulationContext(sim_params=sim_cfg)

Please see the documentation for SimulationCfg for more details on the parameters that can be used to configure the simulation.

Preventing memory leaks in the simulator#

Memory leaks in the Isaac Sim simulator can occur when C++ callbacks are registered with Python objects. This happens when callback functions within classes maintain references to the Python objects they are associated with. As a result, Python’s garbage collection is unable to reclaim memory associated with these objects, preventing the corresponding C++ objects from being destroyed. Over time, this can lead to memory leaks and increased resource usage.

To prevent memory leaks in the Isaac Sim simulator, it is essential to use weak references when registering callbacks with the simulator. This ensures that Python objects can be garbage collected when they are no longer needed, thereby avoiding memory leaks. The weakref module from the Python standard library can be employed for this purpose.

For example, consider a class with a callback function on_event_callback that needs to be registered with the simulator. If you use a strong reference to the MyClass object when passing the callback, the reference count of the MyClass object will be incremented. This prevents the MyClass object from being garbage collected when it is no longer needed, i.e., the __del__ destructor will not be called.

import omni.kit

class MyClass:
    def __init__(self):
        app_interface = omni.kit.app.get_app_interface()
        self._handle = app_interface.get_post_update_event_stream().create_subscription_to_pop(
            self.on_event_callback
        )

    def __del__(self):
        self._handle.unsubscribe()
        self._handle = None

    def on_event_callback(self, event):
        # do something with the message

To fix this issue, it’s crucial to employ weak references when registering the callback. While this approach adds some verbosity to the code, it ensures that the MyClass object can be garbage collected when no longer in use. Here’s the modified code:

import omni.kit
import weakref

class MyClass:
    def __init__(self):
        app_interface = omni.kit.app.get_app_interface()
        self._handle = app_interface.get_post_update_event_stream().create_subscription_to_pop(
            lambda event, obj=weakref.proxy(self): obj.on_event_callback(event)
        )

    def __del__(self):
        self._handle.unsubscribe()
        self._handle = None

    def on_event_callback(self, event):
        # do something with the message

In this revised code, the weak reference weakref.proxy(self) is used when registering the callback, allowing the MyClass object to be properly garbage collected.

By following this pattern, you can prevent memory leaks and maintain a more efficient and stable simulation.

Understanding the error logs from crashes#

Many times the simulator crashes due to a bug in the implementation. This swamps the terminal with exceptions, some of which are coming from the python interpreter calling __del__() destructor of the simulation application. These typically look like the following:

...

[INFO]: Completed setting up the environment...

Traceback (most recent call last):
File "source/standalone/workflows/robomimic/collect_demonstrations.py", line 166, in <module>
    main()
File "source/standalone/workflows/robomimic/collect_demonstrations.py", line 126, in main
    actions = pre_process_actions(delta_pose, gripper_command)
File "source/standalone/workflows/robomimic/collect_demonstrations.py", line 57, in pre_process_actions
    return torch.concat([delta_pose, gripper_vel], dim=1)
TypeError: expected Tensor as element 1 in argument 0, but got int
Exception ignored in: <function _make_registry.<locals>._Registry.__del__ at 0x7f94ac097f80>
Traceback (most recent call last):
File "../orbit/_isaac_sim/kit/extscore/omni.kit.viewport.registry/omni/kit/viewport/registry/registry.py", line 103, in __del__
File "../orbit/_isaac_sim/kit/extscore/omni.kit.viewport.registry/omni/kit/viewport/registry/registry.py", line 98, in destroy
TypeError: 'NoneType' object is not callable
Exception ignored in: <function _make_registry.<locals>._Registry.__del__ at 0x7f94ac097f80>
Traceback (most recent call last):
File "../orbit/_isaac_sim/kit/extscore/omni.kit.viewport.registry/omni/kit/viewport/registry/registry.py", line 103, in __del__
File "../orbit/_isaac_sim/kit/extscore/omni.kit.viewport.registry/omni/kit/viewport/registry/registry.py", line 98, in destroy
TypeError: 'NoneType' object is not callable
Exception ignored in: <function SettingChangeSubscription.__del__ at 0x7fa2ea173e60>
Traceback (most recent call last):
File "../orbit/_isaac_sim/kit/kernel/py/omni/kit/app/_impl/__init__.py", line 114, in __del__
AttributeError: 'NoneType' object has no attribute 'get_settings'
Exception ignored in: <function RegisteredActions.__del__ at 0x7f935f5cae60>
Traceback (most recent call last):
File "../orbit/_isaac_sim/extscache/omni.kit.viewport.menubar.lighting-104.0.7/omni/kit/viewport/menubar/lighting/actions.py", line 345, in __del__
File "../orbit/_isaac_sim/extscache/omni.kit.viewport.menubar.lighting-104.0.7/omni/kit/viewport/menubar/lighting/actions.py", line 350, in destroy
TypeError: 'NoneType' object is not callable
2022-12-02 15:41:54 [18,514ms] [Warning] [carb.audio.context] 1 contexts were leaked
../orbit/_isaac_sim/python.sh: line 41: 414372 Segmentation fault      (core dumped) $python_exe "$@" $args
There was an error running python

This is a known error with running standalone scripts with the Isaac Sim simulator. Please scroll above the exceptions thrown with registry to see the actual error log.

In the above case, the actual error is:

Traceback (most recent call last):
File "source/standalone/workflows/robomimic/tools/collect_demonstrations.py", line 166, in <module>
    main()
File "source/standalone/workflows/robomimic/tools/collect_demonstrations.py", line 126, in main
    actions = pre_process_actions(delta_pose, gripper_command)
File "source/standalone/workflows/robomimic/tools/collect_demonstrations.py", line 57, in pre_process_actions
    return torch.concat([delta_pose, gripper_vel], dim=1)
TypeError: expected Tensor as element 1 in argument 0, but got int

Tricks and Troubleshooting

Contents

Tricks and Troubleshooting#

Checking the internal logs from the simulator#

Using CPU Scaling Governor for performance#

Observing long load times at the start of the simulation#

Receiving a “PhysX error” when running simulation on GPU#

Preventing memory leaks in the simulator#

Understanding the error logs from crashes#