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Device Losses in X-Plane

Introduction

Device losses are a known but difficult to analyze problem in X-Plane. The goal is to explain the nature of device losses, their causes, debugging challenges, and measures for problem resolution.

Definition and Causes

A device loss is a crash of the Graphics Processing Unit (GPU), similar to a software crash on the CPU, but with specific challenges. GPUs execute shaders - small programs that handle tasks such as vertex data transformation, pixel calculations, or object culling. X-Plane uses numerous shader modules, each containing many shader variants. A device loss occurs when a shader or GPU command is executed incorrectly, signaled by the Vulkan error code VK_ERROR_DEVICE_LOST.

Debugging Challenges

Debugging device losses is complex due to the following factors:

  1. Asynchronous Execution: CPU and GPU work asynchronously, with the CPU often several frames ahead. A crash is only detected with delay, making cause analysis difficult.
  2. Limited Debugging Tools: Shaders cannot be inspected step by step. The GPU state is only accessible after execution, and in case of a crash, often only fragmented data is available.
  3. Latency in Detection: The operating system and graphics driver prioritize GPU recovery, leading to delays and visual artifacts before X-Plane registers the error.

Problem Resolution Measures

For investigating device losses, the command line parameter --aftermath is recommended (see also Configuration → GPU Debugging for a quick CLI reference). This activates the Aftermath library (supported for Nvidia, AMD, and Intel GPUs), which collects detailed diagnostic data. When a crash occurs, the message "Encountered a GPU crash!" is displayed, and the collected data helps developers identify the cause. However, Aftermath causes a performance impact and should be used selectively.

In X-Plane 12.2, Aftermath support was revised to insert checkpoints into the command stream for each draw or dispatch command. This fine-grained data enables more precise analysis of the GPU state after a crash. Earlier versions such as 12.06 and 12.1.0 significantly reduced device losses, for example through workarounds for Nvidia driver bugs.

Misunderstandings

A common misconception is that device losses are caused by insufficient video memory (VRAM) - this is not the case. Plugins or scenery can only indirectly trigger device losses, for example through modifications to shader paths. A/B testing with disabled plugins is helpful for reproducible crashes but often ineffective for rare device losses.

Conclusion

Device losses in X-Plane are GPU crashes that are difficult to debug due to the complexity of shaders and asynchronous CPU-GPU interaction. Tools like Aftermath and improved implementations in X-Plane 12.2 facilitate diagnosis. Users can contribute to problem resolution by submitting crash reports with Aftermath enabled. Future developments may further reduce the frequency of such errors.

Further Reading

Topic Page Focus
Configuration Configuration Vulkan settings, shader cache, CLI parameters
Performance Analysis Performance Analysis MangoHUD and GPU monitoring for crash detection
GPU & VRAM GPU & VRAM GPU architecture, VRAM management concepts
Nvidia Drivers Nvidia Drivers Driver versions affecting device loss frequency
Display Server Display Server Compositor and GPU interaction
System Monitoring Monitoring dmesg, journalctl for GPU error analysis

Sources