What makes Ruby slow?
Ruby is slow at certain things. But what parts of it are the most problematic?
How much does the garbage collector affect performance? I know I've had times when running the garbage collector alone took several seconds, especially when working with OpenGL libraries.
I've used matrix math libraries with Ruby that were particularly slow. Is there an issue with how ruby implements basic math?
Are there any dynamic features in Ruby that simply cannot be implemented efficiently? If so, how do other languages like Lua and Python solve these problems?
Has there been recent work that has significantly improved performance?
Answer
Ruby is slow. But what parts of it are the most problematic?
It does "late lookup" for methods, to allow for flexibility. This slows it down quite a bit. It also has to remember variable names per context to allow for eval, so its frames and method calls are slower. Also it lacks a good JIT compiler currently, though MRI 1.9 has a bytecode compiler (which is better), and jruby compiles it down to java bytecode, which then (can) compile via the HotSpot JVM's JIT compiler, but it ends up being about the same speed as 1.9.
How much does the garbage collector effect performance? I know I've had times when running the garbage collector alone took several seconds, especially when working with OpenGL libraries.
from some of the graphs at http://www.igvita.com/2009/06/13/profiling-ruby-with-googles-perftools/ I'd say it takes about 10% which is quite a bit--you can decrease that hit by increasing the malloc_limit in gc.c and recompiling.
I've used matrix math libraries with Ruby that were particularly slow. Is there an issue with how ruby implements basic math?
Ruby 1.8 "didn't" implement basic math it implemented Numeric classes and you'd call things like Fixnum#+ Fixnum#/ once per call--which was slow. Ruby 1.9 cheats a bit by inlining some of the basic math ops.
Are there any dynamic features in Ruby that simply cannot be implemented efficiently? If so, how do other languages like Lua and Python solve these problems?
Things like eval are hard to implement efficiently, though much work can be done, I'm sure. The kicker for Ruby is that it has to accomodate for somebody in another thread changing the definition of a class spontaneously, so it has to be very conservative.
Has there been recent work that has significantly improved performance?
1.9 is like a 2x speedup. It's also more space efficient. JRuby is constantly trying to improve speed-wise [and probably spends less time in the GC than KRI]. Besides that I'm not aware of much except little hobby things I've been working on. Note also that 1.9's strings are at times slower because of encoding friendliness.