How we added WebGPU without affecting performance (Web Engines Hackfest '24)

The Nugget

Adding WebGPU to Deno without impacting startup performance involved using lazy-loaded modules, which are loaded only when first accessed, effectively managing increased snapshot sizes and startup times.

Make it stick

🚀 Lazy-loading modules: Only load the modules when they are needed, reducing initial load time.
🧩 Micro-optimizations add up: A 0.5-millisecond improvement in startup time was crucial despite seeming minor.
💡 Single-use efficiency: Users of WebGPU, mainly for intensive applications, can tolerate a one-time startup cost.
🛠️ Shared code base challenge: Managing multiple repositories so both Deno and Mozilla could iterate independently.

The WebGPU API, a successor to WebGL, provides a lower-level, more efficient API.
Originating from a 2017 proposal by Apple, it was later shaped by merging proposals from Mozilla (Obsidian) and Google (NXT).
WGPU is Mozilla's implementation of the WebGPU specification, created by Dimitri Mal Khronos.

Deno's layered architecture starts with Rust bindings to V8 (rusty V8) and adds utility functions (Deno Core), extensions (fetch, crypto, WebGPU), and the runtime that integrates all components.
WebGPU's JavaScript part is significant (205 kB), impacting startup time and complexity.

WebGPU integration faced increased snapshot size and startup time. The initial implementation increased startup time from 14 milliseconds to 19 milliseconds.
Due to community feedback and performance concerns, the WebGPU API was temporarily removed for over six months in 2023.

Addressed startup time issue by weakly linking framework dependencies like Metal, reducing startup time by approximately 0.5 milliseconds.
Created lazy-loaded modules: Modules are loaded only upon first access, spreading the load and minimizing startup impact.
Even though lazy-loading increased memory usage and compile time slightly, it was a justified trade-off.

Ongoing effort to further optimize startup time by refining weak linking of frameworks.
Running conformance tests for WebGPU and supporting additional APIs like offscreen canvas and canvas rendering context in Deno.
Collaboration potential with Servo for improved performance.

"The main issue was due to size increase and increase of the JS snapshot size, leading to increased startup time."
"We created a lazy loader... it loads the module once and stores the value for subsequent calls."
"For WebGPU, making a one-time small initialization trade-off is viable since its user base is very niche."
"Patch dependencies to weakly link frameworks saved 0.5 milliseconds of startup time; every bit counts."

This summary contains AI-generated information and may have important inaccuracies or omissions.