The author experienced system hangs on wake-up with their AMD GPU on Linux. They traced the issue to the AMDGPU driver's handling of the PCIe link and power states during suspend and resume. Specifically, the driver was prematurely powering off the GPU before the system had fully suspended, leading to a deadlock. By patching the driver to ensure the GPU remained powered on until the system was fully asleep, and then properly re-initializing it upon waking, they resolved the hanging issue. This fix has since been incorporated upstream into the official Linux kernel.
The blog post "I helped fix sleep-wake hangs on Linux with AMD GPUs" by nyanpasu64 details the author's journey in troubleshooting and ultimately contributing to a solution for a persistent issue: systems with AMD GPUs frequently hanging during suspend/resume cycles on Linux.
The author meticulously documented their troubleshooting process, starting with the observation that their system would reliably freeze after resuming from sleep. They utilized various debugging tools, including journalctl for examining system logs, and progressively narrowed down the problem. Initially suspecting kernel modules related to sound and Bluetooth, they systematically eliminated those possibilities. The author's attention then shifted to the AMDGPU driver, particularly the behavior of the display during suspend and resume.
A crucial clue emerged when they discovered the system would resume successfully if an external monitor remained connected during sleep. This observation led them to hypothesize that the issue was linked to the driver's handling of display power management, specifically when dealing with laptop internal displays that are powered off during sleep.
Further investigation, aided by tools like amdgpu.dpm=0 (which disables dynamic power management), reinforced this hypothesis. They pinpointed the problem to a race condition within the AMDGPU driver. This race condition occurred during the resume sequence: the system attempted to initialize the display before the GPU was fully ready, leading to a system hang.
The author then embarked on understanding the intricacies of the AMDGPU driver code, meticulously tracing the execution flow related to display initialization and power management during resume. This involved studying the driver's interaction with the Direct Rendering Manager (DRM) subsystem and the kernel's device power management framework.
Armed with this understanding, the author proposed a solution: delaying the initialization of the display until after the GPU had fully resumed. They implemented this fix by modifying the driver code to ensure proper sequencing of operations during the resume process, effectively eliminating the race condition.
After thorough testing and refinement, the author submitted their patch to the Linux kernel mailing list. The patch was reviewed by kernel maintainers, further refined through collaborative discussion, and ultimately accepted and integrated into the mainline kernel. Thus, the author successfully contributed to resolving a widespread and frustrating issue affecting numerous Linux users with AMD GPUs, demonstrating the power of persistent troubleshooting, detailed analysis, and community collaboration in open-source software development. The blog post concludes with a reflection on the author's learning experience and the satisfaction of contributing back to the Linux community.
Summary of Comments ( 31 )
https://news.ycombinator.com/item?id=43071983
Commenters on Hacker News largely praised the author's work in debugging and fixing the AMD GPU sleep/wake hang issue. Several expressed having experienced this frustrating problem themselves, highlighting the real-world impact of the fix. Some discussed the complexities of debugging kernel issues and driver interactions, commending the author's persistence and systematic approach. A few commenters also inquired about specific configurations and potential remaining edge cases, while others offered additional technical insights and potential avenues for further improvement or investigation, such as exploring runtime power management. The overall sentiment reflects appreciation for the author's contribution to improving the Linux AMD GPU experience.
The Hacker News post discussing the blog post "I helped fix sleep-wake hangs on Linux with AMD GPUs" has generated a moderate number of comments, mostly focusing on technical details and personal experiences with similar issues.
Several commenters share their own struggles with AMD GPUs and sleep/resume cycles on Linux. They express gratitude for the author's work and describe the frustration these bugs have caused. One user mentions experiencing similar issues with an older kernel and a specific AMD GPU model, highlighting the pervasiveness of such problems. Another recounts their experience with a laptop constantly crashing due to similar problems, even after trying numerous suggested fixes, eventually leading them to switch to an Intel-based machine.
A few comments delve into the technical aspects of the bug and the fix. One commenter questions the root cause of the problem, suggesting it might be related to the handling of DisplayPort Multi-Stream Transport (MST). They discuss the challenges in debugging these types of issues, particularly the intermittent nature of the hangs. Another commenter with deep knowledge of the Linux kernel discusses the complexity of power management and speculates about the interplay between different components and drivers. They highlight the difficulty of pinpointing the exact source of such bugs and praise the author's persistence in tracking down the problem.
Some comments also touch upon the broader topic of AMD GPU driver stability on Linux. One user expresses a general sentiment of frustration with the perceived instability of AMD drivers compared to Nvidia's, acknowledging the open-source nature of the AMD drivers as a contributing factor to the complexity.
Overall, the comments section reflects a mixture of appreciation for the author's contribution, shared experiences of frustration with similar issues, and technical discussion surrounding the complexities of debugging and fixing such bugs in the Linux kernel and AMD drivers. The comments don't offer significantly differing viewpoints on the core issue, but rather provide different perspectives on the problem's impact and the challenges involved in resolving it.