The blog post explores how to parallelize the ./configure step in software builds, primarily focusing on GNU Autotools-based projects. It highlights that while the make step is commonly parallelized, the configure step often runs serially, creating a bottleneck, especially on multi-core systems. The author presents a method using GNU parallel to distribute the configuration of subdirectories within a project's source tree, significantly reducing the overall configure time. This involves creating a wrapper script that intercepts configure calls and uses parallel to execute them concurrently across available cores. While acknowledging potential pitfalls like race conditions and broken dependencies between subdirectories, the author suggests this technique offers a generally safe and effective way to accelerate the configuration stage for many projects.
This blog post by Tavian Barnes explores the intricacies of parallelizing the ./configure step in the build process of software, particularly focusing on projects that utilize the GNU Autotools system. The author begins by explaining the typical ./configure process, emphasizing its sequential nature where tests are executed one after another, often probing for the presence or absence of specific system libraries, header files, and functionalities. This sequential execution, while reliable, becomes a bottleneck, especially on multi-core systems where parallel processing could significantly reduce the overall configuration time.
The post then dives into the challenges of parallelizing ./configure. A naive approach of simply running multiple tests concurrently can lead to incorrect results due to race conditions and dependencies between tests. For instance, one test might rely on the results of a previous test, and concurrent execution could disrupt this dependency, leading to inaccurate configuration. The author highlights that while some build systems offer limited parallelization within specific configuration tests, true parallelization of the entire ./configure process is complex.
The core of the post centers around a detailed explanation of a patch developed by the author that introduces parallel execution to the ./configure script. This patch, applicable to projects using Autoconf, leverages a job server model. The patch modifies the generated configure script to spawn a pool of worker processes. These workers execute individual tests assigned by the main configure process, ensuring that dependencies between tests are respected. The results from each worker are then collected and processed by the main process. The post meticulously dissects the implementation details of the patch, including how the job server is managed, how inter-process communication is handled, and how the patch avoids race conditions.
Furthermore, the author addresses the potential limitations and caveats of the parallel ./configure approach. The overhead of managing the job server and inter-process communication can sometimes outweigh the benefits of parallelization, especially for projects with a small number of configuration tests. The post also acknowledges the potential for increased complexity in debugging issues arising from parallel execution.
Finally, the author provides benchmark results demonstrating the performance improvements achieved with the parallel ./configure patch on various projects. These results showcase a significant reduction in configuration time, particularly on multi-core systems, highlighting the potential of this optimization. The post concludes by offering insights into the practical application of the patch and suggesting potential future improvements to further enhance the parallelization of the ./configure process.
Summary of Comments ( 132 )
https://news.ycombinator.com/item?id=43799396
Hacker News users discussing Tavianator's "Parallel ./configure" post largely focused on the surprising lack of parallel configure scripts by default. Many commenters shared similar experiences of manually parallelizing configure processes, highlighting the significant time savings, especially with larger projects. Some suggested reasons for this absence include the perceived complexity of implementing robust parallel configure scripts across diverse systems and the potential for subtle errors due to dependencies between configuration checks. One user pointed out that Ninja's recursive make implementation offers a degree of parallelism during the build stage, potentially mitigating the need for parallel configuration. The discussion also touched upon alternative build systems like Meson and CMake, which generally handle parallelism more effectively.
The Hacker News post "Parallel ./configure" with the ID 43799396 discusses the linked blog post about making the
./configurestep in software builds faster, specifically by parallelizing it. The comments section contains several interesting points.One commenter points out that the proposed method primarily benefits projects that are already using recursive Make, and suggests that projects not using recursive Make could see even greater speedups by adopting it. They explain that the core issue isn't
./configureitself being slow, but rather the repeated execution of small programs it invokes to probe system capabilities. Recursive Make helps by allowing these probes to run in parallel within subdirectories.Another commenter mentions that Meson, a popular build system, already incorporates many of these techniques by design. They argue that Meson's approach offers additional advantages, including cross-compilation support and a simpler syntax. This comment sparks a brief discussion about the merits of different build systems and whether the techniques discussed in the article could be backported to autoconf-based projects.
Some users express skepticism about the real-world benefits of parallelizing
./configure, arguing that it's often not the bottleneck in the build process. They suggest that optimizing other parts of the build, such as compilation, would yield more significant improvements.One user shares their experience of using a similar approach with the Ninja build system and highlights the importance of ensuring correct dependency tracking to prevent race conditions during the configuration process.
Another commenter raises the point that the number of CPU cores available might not be the limiting factor for configuration speed. They suggest that I/O operations, such as disk access, could be the real bottleneck, especially in virtualized environments.
Finally, a few commenters discuss the challenges of parallelizing
./configurein complex projects with intricate dependencies between configuration tests. They point out that simply running tests in parallel without proper synchronization could lead to incorrect results or build failures.