The big news, however, is the recent announcement by the Chakra team that they are working on adding specific asm.js optimizations, to arrive in Windows 10 together with the other optimizations mentioned earlier. These optimizations haven’t made it to the Preview channel yet, so we can’t measure and report on them here. However, we can speculate on the improvements based on the initial impact of landing asm.js optimizations in Firefox. As shown in this benchmark comparisons slide containing measurements from right after the landing, asm.js optimizations immediately brought Firefox to around 2x slower than native performance (from 5-12x native before). Why should these wins translate to Chakra? Because, as explained in our previous post, the asm.js spec provides a predictable way to validate asm.js code and generate high-quality code based on the results.
So, here’s looking forward to good asm.js performance in Windows 10!
As we mentioned before, the initial landing of asm.js optimizations in Firefox generally put Firefox within 2x of native in terms of raw throughput. By the end of 2013, we were able to report that the gap had shrunk to around 1.5x native – which is close to the amount of variability that different native compilers have between each other anyhow, so comparisons to “native speed” start to be less meaningful.
- a new register allocation algorithm, based on the new register allocator in LLVM 3.0: while speedups vary, one notable example is an initial 20% improvement on x86 on the zlib portion of Google’s Octane benchmark and another 4% after refinement; and
- effective address optimizations: a recent addition in Firefox Nightly, producing 5% – 10% speedups across heap-access-heavy workloads.
Separate from all these throughput optimizations, there have also been a set of load time optimizations in Firefox: off-main-thread and parallel compilation of asm.js code as well as caching of the compiled machine code. As described in this post, these optimizations significantly improve the experience of starting a Unity- or Epic-sized asm.js application. Existing asm.js workloads in the benchmarks mentioned above do not test this aspect of asm.js performance so we put together a new benchmark suite named Massive that does. Looking at Firefox’s Massive score over time, we can see the load-time optimizations contributing to a more than 6x improvement (more details in the Hacks post introducing the Massive benchmark).
The Bottom Line
What is most important, in the end, are not the underlying implementation details, nor even specific performance numbers on this benchmark or that. What really matters is that applications run well. The best way to check that is to actually run real-world games! A nice example of an asm.js-using game is Dead Trigger 2, a Unity 3D game:
The video shows the game running on Firefox, but as it uses only standard web APIs, it should work in any browser. We tried it now, and it renders quite smoothly on Firefox, Chrome and Safari. We are looking forward to testing it on the next Preview version of Internet Explorer as well.
Another example is Cloud Raiders:
As with Unity, the developers of Cloud Raiders were able to compile their existing C++ codebase (using Emscripten) to run on the web without relying on plugins. The result runs well in all four of the major browsers.
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