Raytracing Experience Report

[Ethan McCue]

Continuing from this, I ran it against the reference C++ implementation and
got these numbers.

# Reference C++ implementation (-O3)

```
real 6m35.702s
user 6m33.780s
sys 0m1.454s
```

# Java With Value Classes

```
real 11m50.122s
user 11m36.536s
sys 0m13.281s
```

# Java Without Value Classes

```
real 17m1.038s
user 16m40.993s
sys 0m29.400s
```

I am wondering if using an AOT cache could help catch up to the C++, but I
get a class file version error running with -XX:AOTCache=value.aot

Error: LinkageError occurred while loading main class Main
        java.lang.UnsupportedClassVersionError: Main has been compiled by a
more recent version of the Java Runtime (class file version 70.0), this
version of the Java Runtime only recognizes class file versions up to 69.0

On Wed, Oct 29, 2025 at 3:44 PM Sergey Kuksenko <sergey.kuksenko at oracle.com>
wrote:

> Hi Ethan,
>
> Thank you for the information. Your example and the code are pretty
> straightforward, and I was able to repeat and diagnose the issue.
>
> The fact is, the performance issue is not directly related to value
> classes. The problem is that HittableList::hit method (invoked at
> Camera::rayColor) was inlined by JIT in the non-value version and wasn't
> inlined in the value classes version.
> When you inline that invocation manually, you should get the same
> performance for both versions.
> HittableList::hit was not inlined in the value classes version because
> value classes resulted in a different code size and changed the inline
> heuristics. It's a mainline issue; you'll encounter it quite rarely.
> Current inline heuristics work well in 99% of cases, and you should be very
> lucky (or unlucky) to get it in real life.
>
> Best regards,
> Sergey Kuksenko
>
>
>
> ________________________________________
> From: valhalla-dev <valhalla-dev-retn at openjdk.org> on behalf of Ethan
> McCue <ethan at mccue.dev>
> Sent: Monday, October 27, 2025 5:08 PM
> To: valhalla-dev at openjdk.org
> Subject: Raytracing Experience Report
>
> Hi all,
>
> I have been following along in the "Ray Tracing in a Weekend" book and
> trying to make as many classes as possible value classes. (Vec3, Ray, etc.)
>
> https://github.com/bowbahdoe/raytracer
>
> https://raytracing.github.io/books/RayTracingInOneWeekend.html
>
> (without value classes)
>
> time java --enable-preview --class-path build/classes Main > image.ppm
>
> real 4m33.190s
> user 4m28.984s
> sys 0m5.511s
>
> (with value classes)
>
> time java --enable-preview --class-path build/classes Main > image.ppm
>
> real 3m54.623s
> user 3m52.205s
> sys 0m2.064s
>
> So by the end the version using value classes beats the version without
> them by ~14% using unscientific measurements.
>
> But that is at the end, running the ray tracer on a relatively large scene
> with all the features turned on. Before that point there were some
> checkpoints where using value classes performed noticeably worse than the
> equivalent code sans the value modifier
>
> https://github.com/bowbahdoe/raytracer/tree/no-value-faster
>
> real 1m22.172s
> user 1m9.871s
> sys 0m12.951s
>
> https://github.com/bowbahdoe/raytracer/tree/with-value-slower
>
> real 3m34.440s
> user 3m19.656s
> sys 0m14.870s
>
> So for some reason just adding value to the records/classes makes the
> program run a over 2x as slow.
>
>
> https://github.com/bowbahdoe/raytracer/compare/no-value-faster...with-value-slower
>
> Is there some intuition that explains this? I am on a stock M1 Arm Mac.
>
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