A Multi-threaded Go Raytracer


Above is the output of the raytracer. Below is a diagnostic mode showing which goroutines raytraced which section of the screen. Each goroutine has its own color to outline the pixels it traces:



I wrote a simple multi-threaded ray tracer in Google's new "go" language. It's an adaptation of Flying Frog Consultancy's Raytracer.

It runs single-threaded about 1/2 the speed of a comparable C++ version. I guess the C++ version benefits from a more optimizing compiler and the ability to inline small functions.

Compared to ordinary C/C++, the Go version was easier to multithread.

On my dual-core Macbook Pro I get an 1.80x speedup when running with GOMAXPROCS > 1:

$ GOMAXPROCS=1 time ./gotrace
1.52 real 1.50 user 0.01 sys
$ GOMAXPROCS=2 time ./gotrace
0.82 real 1.50 user 0.01 sys
$ GOMAXPROCS=3 time ./gotrace
0.81 real 1.50 user 0.01 sys

On an eight-core, 16 Hyperthread HP Z600 running Ubuntu 9.10, (with the source code changed to use 16 goroutines instead of the default 8 goroutines) I get a 5.8x speedup:

$ GOMAXPROCS=1 time ./gotrace
1.05user 0.01system 0:01.06elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+1544outputs (0major+2128minor)pagefaults 0swaps
$ GOMAXPROCS=16 time ./gotrace
1.32user 0.00system 0:00.18elapsed 702%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+1544outputs (0major+2190minor)pagefaults 0swaps

Source code gotracer.zip


Comments

Sebastian said…
just tried it on my first gen macbook with 32 bit.
works great! thanks for the code

MacBook:gotracer sebi$ GOMAXPROCS=1 time ./gotrace
4.98 real 4.96 user 0.02 sys
MacBook:gotracer sebi$ GOMAXPROCS=2 time ./gotrace
2.60 real 4.96 user 0.02 sys
MacBook:gotracer sebi$ GOMAXPROCS=3 time ./gotrace
2.60 real 4.96 user 0.03 sys
November 10, 2009 at 10:49 PM
Jack Palevich said…
Neat! Glad you liked it.
November 11, 2009 at 1:07 AM
Unknown said…
I managed to improve the speed by about 60% ( on a single core ), bringing the rendering speed down from 2.0s to 1.3s.

Also I noticed that go gets sluggishly slow if pointers are used for the vector math, I could even nail down a single function that will cut the speed in half.

As I intend to post it on the mailing list, and data needs to exchanged, I created a project on gitorious: http://gitorious.org/gotracer.

I mentioned your name everywhere, hoping to make sure authorship is clear. If you truly dislike that please let me know and we will figure out a solution :).

Kind Regards.
November 12, 2009 at 3:46 PM
Jack Palevich said…
No worries, I intended the code to be open sourced, so you're free to develop it any way you like. Glad to hear it inspired you to write some good go code!
November 24, 2009 at 7:34 PM
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