The blog post presents benchmark results comparing input latency between Wayland and X11 using a custom-built input latency measurement tool. It concludes that Wayland exhibits consistently lower input latency than X11 across various desktop environments and configurations, even when accounting for composition latency. The author attributes Wayland's superior performance to its simplified architecture, which bypasses X11's legacy layers and allows for more direct communication between applications and the display server, leading to reduced overhead and quicker processing of input events. While acknowledging potential confounding factors and the limitations of the testing methodology, the results strongly suggest that Wayland delivers a more responsive user experience due to its inherent design advantages in input handling.
This blog post, titled "Hard numbers in the Wayland vs. X11 input latency discussion," delves into the often-debated topic of input latency differences between the Wayland and X11 display server protocols. The author aims to provide concrete data to clarify the performance characteristics of each system, moving beyond anecdotal evidence and subjective experiences. They meticulously detail their experimental setup, which involves a custom-built input latency measurement device consisting of a photodiode pointed at a spinning disk with a white mark. This setup allows precise timing of display updates synchronized with input events.
The author acknowledges the complexity of accurately measuring input latency, emphasizing the importance of a controlled environment and consistent methodology. They outline the various stages involved in processing input events, from the initial hardware interaction to the final pixel rendering on the screen, highlighting potential sources of latency within each stage. Both Wayland and X11 systems are analyzed using the same hardware and testing methodology to ensure a fair comparison.
The experimental results are presented in a table format, showcasing the latency measurements obtained for various scenarios, including both desktop environments (GNOME and KDE) and different compositor implementations (Mutter and KWin). The data reveals that Wayland generally exhibits lower input latency compared to X11, albeit with some variations depending on the specific configuration. The author carefully analyzes the data, discussing potential contributing factors to the observed differences, such as compositor architecture and input handling mechanisms.
Specifically, the results demonstrate that Wayland's more streamlined architecture, which bypasses certain layers present in X11, can contribute to reduced latency. However, the author also notes that the actual latency differences are often small and might not be perceptible in typical usage scenarios. Furthermore, they emphasize that other factors, such as the specific application being used and the overall system configuration, can also influence input latency. Therefore, while Wayland demonstrates a potential for lower latency, it's not a guaranteed improvement in every situation.
The post concludes by reiterating the importance of objective measurements in evaluating performance differences between Wayland and X11. The author emphasizes that while their findings suggest Wayland generally exhibits lower input latency, further research and analysis are necessary to fully understand the intricacies of input latency and its impact on user experience. They encourage further investigation and discussion within the community to refine the methodologies and gain a more comprehensive understanding of this complex topic.
Summary of Comments ( 161 )
https://news.ycombinator.com/item?id=42831509
Hacker News users discussed the methodology and conclusions of the linked article comparing Wayland and X11 input latency. Several commenters questioned the fairness of the comparison, pointing out potential confounding factors like different compositor implementations (Sway vs. GNOME) and varying hardware configurations. Some suggested the benchmark wasn't representative of real-world usage, focusing on synthetic tests rather than common desktop tasks. Others highlighted the difficulty of accurately measuring input latency and the potential for subtle system variations to skew results. A few commenters shared their personal experiences, with some reporting noticeable improvements in latency under Wayland while others experienced no discernible difference. Overall, there was skepticism about the article's definitive claim of Wayland's superiority, with many calling for more rigorous and comprehensive testing.
The Hacker News post titled "Hard numbers in the Wayland vs. X11 input latency discussion" has generated a lively discussion with several insightful comments. Many commenters express appreciation for the author's methodology and the concrete data presented, contrasting it with the often anecdotal nature of previous Wayland vs. X11 latency debates.
Several commenters dive into the technical nuances affecting input latency. One highlights the significance of event processing within the compositor, suggesting that GNOME's Mutter compositor might be a source of latency, not Wayland itself. This is corroborated by another commenter pointing out that Sway, a different Wayland compositor, demonstrates significantly lower latency. This leads to a discussion about the architectural differences between compositors and how they handle input events.
The role of the Linux kernel is also discussed, with one commenter mentioning that kernel bypass techniques like bypassing the input event queue could further reduce latency, even on X11. This sparks a brief tangent about the complexities and potential benefits of such approaches.
Another commenter raises the importance of considering the entire input pipeline, not just the compositor. Factors like the specific input devices, drivers, and even the application receiving the input can all contribute to perceived latency. This holistic perspective is echoed by others, cautioning against attributing all latency issues solely to Wayland or X11.
Some skepticism is expressed regarding the benchmark's methodology. One commenter questions the reliance on visual feedback for latency measurement, suggesting that more precise instrumentation might be necessary for a truly accurate comparison. Another points out the potential variability introduced by background processes and system load.
Several comments focus on the practical implications of input latency. Gamers, in particular, express continued concern about Wayland's performance, citing specific issues with certain games or configurations. However, others counter that Wayland's security advantages and potential for future optimization outweigh the current latency concerns.
Finally, there's a thread discussing the future of Wayland and X11. While acknowledging Wayland's progress, some commenters believe X11 will remain relevant for certain use cases for the foreseeable future. Others express optimism that ongoing development will eventually resolve Wayland's remaining latency issues, leading to its widespread adoption. The overall sentiment seems to be one of cautious optimism about Wayland's potential while acknowledging the current challenges.