Incredibuild Team
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Why Build Cache optimization matters
In modern software development, slow builds waste time and resources. This impacts team’s productivity and delays project timelines. Build caching is a powerful method to accelerate build times by reusing outputs from previous builds and avoiding redundant task execution. However, achieving optimal caching performance isn’t always straightforward. Cache hit rates measure the effectiveness of a build cache by calculating the portion of cache uses, or hits, out of all cacheable build tasks. A high hit rate indicates that the cache is successfully reusing previously executed tasks, leading to faster builds. On the other hand, a low hit rate may suggest possible inefficiencies, such as redundant task execution. Improving cache hits can be challenging, but optimizing these significantly accelerates build speeds and reduces resource consumption.
The video below walks through the fundamentals of optimizing build cache performance with Incredibuild’s Build Monitor. This article serves as both a companion and a reference, providing key takeaways and details for those who prefer exploring at their own pace. We’ll walk through a real-world example and provide actionable strategies to reduce cache misses and enhance overall efficiency. Whether you’re new to build caching or looking to improve your current workflow, this guide has you covered.
Build acceleration basics and common challenges
Incredibuild’s core functionality revolves around breaking down large build tasks into smaller, manageable tasks, caching or retrieving already run tasks from cache and distributing the rest across multiple machines. Build caching works by storing the outputs of these previously executed tasks and reusing
them in subsequent builds. This reduces redundant processing, saving both time and computational resources.
Cache Hits vs. Cache Misses:
· Cache Hits: When a task’s output is successfully retrieved from the cache.
· Cache Misses: When a task needs to be re-executed, either due to code changes or inefficiencies.
Some cache misses are normal and cannot be avoided. For example, misses caused by legitimate code changes are normal. However, inefficiencies—such as poorly designed dependency management or issues with autogenerated code—can lead to avoidable misses, slowing down your builds unnecessarily.
Introducing Incredibuild’s Build Monitor
Incredibuild’s Build Monitor provides the observability needed to optimize build cache performance. With its intuitive visual tools, you can:
· Identify cache activity using dedicated bars
· Monitor resource utilization using build graphs to detect potential performance bottlenecks.
· Examine detailed task counters to identify unexpected misses.
· Leverage automatic and detailed reports to investigate specific cache misses.
These features empower teams to dive deep into their builds and identify areas for improvement. To see how this works in practice, let’s explore a real-world example.
Real-life example: analyzing cache behavior with Kodi
To illustrate the power of Build Monitor, we’ll look at a series of builds using the open-source Kodi project.
First build:
During the initial build of the Kodi project, the cache was populated for the first time. This meant that every task executed was an expected cache miss, as no outputs had yet been stored in the cache. The build took approximately 6 minutes to complete, with activity visible in the build cache bars as tasks were added to the cache. This first build, already accelerated by distribution, also sets the foundation for improved performance by cache in subsequent runs.
· During the initial build, the cache is populated for the first time. This results in cache misses for all tasks as their outputs are generated and stored.
· Build time: ~6 minutes.
· Observations: Cache bars show “investment” activity as tasks are executed and added to the cache.
Subsequent build:
During the subsequent build of the Kodi project, the previously populated cache comes into play. With no new code changes introduced, Incredibuild utilizes the cached outputs to skip redundant task executions. This results in a significant reduction in build time and needed compute, down to approximately 2.5 minutes. The cache bars prominently display a high rate of cache hits, highlighting the efficiency gained by leveraging the cached data. This build underscores the value of an optimized build cache, demonstrating how it transforms performance for recurring builds.
· Without any code changes, the next build takes advantage of the populated cache, significantly reducing build time.
· Build time: ~2.5 minutes.
· Observations: Cache bars now reflect a high rate of cache hits, showcasing the benefits of a well-utilized cache.
Build with code changes:
When code changes were introduced in the Kodi project, the build process required re-executing a significant portion of tasks, leading to a longer build time of approximately 4 minutes. The Build Monitor highlighted these changes by showing a lower cache hit rate and identified the specific tasks affected. For example, modifications in precompiled headers (PCH) caused cache misses and necessitated recompilation. This step demonstrated how Build Monitor’s observability tools provide detailed insights into why cache misses occur, helping developers address inefficiencies effectively.
· When code changes are introduced, the build duration increases (~4 minutes) due to new cache misses.
· Observations: Build Monitor highlights the affected tasks and provides insights into the reasons for these misses, such as changes in a header file, causing a recompiling of a precompiled header (PCH).
Deep Dive: investigating cache misses and resolving issues
Cache misses aren’t always avoidable, but identifying and addressing inefficiencies can dramatically improve performance. Here’s a common scenario involving autogenerated code.
Problem: Autogenerated code with changing pattern (timestamp, i.e.) can cause consistent cache misses, as each build treats the file as new.
Solution:
1. Use Build Monitor’s detailed reports to identify tasks affected by the autogenerated code.
2. Examine the file in question. For example, in one case, a timestamp was being updated in the autogenerated file, triggering unnecessary re-execution.
3. Modify the code to improve cache compatibility. By avoiding the changing code, or containing it in a minimal scope, we can get hits. Build Cache can also ignore leading comments in the code. When making sure such changing patterns are limited to the leading comment Build cache can convert these to cache hits.
4. Validate the changes with subsequent builds, ensuring the issue is resolved.
Outcome: By addressing the root cause, developers can achieve full cache hits for the affected tasks, significantly reducing build times.
General strategies for Build Cache optimization
While the Kodi example highlights specific techniques, Incredibuild’s Build Monitor is versatile enough to address a wide range of cache inefficiencies. Here are some general tips:
1. Analyze Patterns: Use Build Monitor’s reports to identify recurring misses and investigate their causes.
2. Enable Full Report Mode: For deeper insights, switch from automatic to full reporting to capture details for all tasks.
3. Review Build Settings: Misconfigured settings can lead to avoidable inefficiencies.
4. Optimize Dependencies: Ensure that frequently changing dependencies are handled in a way that minimizes unnecessary task execution.
Why invest in Build Cache optimization?
Optimizing build cache performance is a long-term investment that pays dividends in:
· Time Savings: Faster builds free up developers to focus on innovation.
· Resource Efficiency: Reduced computational demands lower costs and environmental impact.
· Team Productivity: Improved builds mean fewer disruptions to workflows.
Incredibuild’s Build Monitor provides the tools you need to make this optimization process straightforward and effective.
Build cache optimization is essential for efficient development workflows, and Incredibuild’s Build Monitor simplifies the process of identifying and resolving cache inefficiencies. By leveraging its powerful observability features, teams can achieve faster builds, better resource utilization, and smoother development cycles.
Ready to optimize your builds? Watch the video embedded below for a detailed walkthrough, and explore how Incredibuild can transform your development process.
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