Making ruby program run on all processors

Question

I've been looking at optimizing a ruby program that's quite calculation intensive on a lot of data. I don't know C and have chosen Ruby (not that I know it well either) and I'm quite happy with the results, apart from the time it takes to execute. It is a lot of data, and without spending any money, I'd like to know what I can do to make sure I'm maximizing my own systems resources.

When I run a basic Ruby program, does it use a single processor? If I have not specifically assigned tasks to a processor, Ruby won't read my program and magically load each processor to complete the program as fast as possible will it? I'm assuming no...

I've been reading a bit on speeding up Ruby, and in another thread read that Ruby does not support true multithreading (though it said JRuby does). But, if I were to "break up" my program into two chunks that can be run in separate instances and run these in parralel...would these two chunks run on two separate processors automatically? If I had four processors and opened up four shells and ran four separate parts (1/4) of the program - would it complete in 1/4 the time?

Update

After reading the comments I decided to give JRuby a shot. Porting the app over wasn't that difficult. I haven't used "peach" yet, but just by running it in JRuby, the app runs in 1/4 the time!!! Insane. I didn't expect that much of a change. Going to give .peach a shot now and see how that improves things. Still can't believe that boost.

Update #2

Just gave peach a try. Ended up shaving another 15% off the time. So switching to JRuby and using Peach was definitely worth it.

Thanks everyone!

Without seeing source code we're guessing what could be done to speed up your application. It might be possible to speed it quite a bit though, if you're doing some things the hard/slow way. — the Tin Man, Nov 12 '12 at 21:59

score 4 · Accepted Answer · answered Nov 12 '12 at 22:50

Use JRuby and the peach gem, and it couldn't be easier. Just replace an .each with .peach and voila, you're executing in parallel. And there are additional options to control exactly how many threads are spawned, etc. I have used this and it works great.

You get close to n times speedup, where n is the number of CPUs/cores available. I find that the optimal number of threads is slightly more than the number of CPUs/cores.

score 2 · Answer 2 · answered Nov 12 '12 at 20:14

Like others have said the MRI implementation of ruby (the one most people use) does not support native threads. Hence you can not split work between CPU cores by launching more threads using the MRI implementation.

However if your process is IO-bound (restricted by disk or network activity for example), then you may still benefit from multiple MRI-threads.

JRuby on the other hand does support native threads, meaning you can use threads to split work between CPU cores.

But all is not lost. With MRI (and all the other ruby implementations), you can still use processes to split work.

This can be done using Process.fork for example like this:

Process.fork {
  10.times {
    # Do some work in process 1
    sleep 1
    puts "Hello 1"
  }
}

Process.fork {
  10.times {
    # Do some work in process 2
    sleep 1
    puts "Hello 2"
  }
}

# Wait for the child processes to finish
Process.wait

Using fork will split the processing between CPU cores, so if you can live without threads then separate processes are one way to do it.

score 0 · Answer 3 · edited May 23 '17 at 12:09

Threading is usually considered one of Ruby's weak points, but it depends more on which implementation of Ruby you use.

A really good writeup on the different threading models is "Does ruby have real multithreading?".

From my experience and from what I gathered from people who know better about this stuff, it seems if you are going to chose a Ruby implementation, JRuby is the way to go. Though, if you are learning Ruby you might want to chose another language such has Erlang, or maybe Clojure, which are popular choices if you wanting to use the JVM.

score 0 · Answer 4 · answered Nov 12 '12 at 20:09

As nice as ruby is, it's not known for its speed of execution. That being said, if, as noted in your comment, you can break up the input into equal-sized chunks you should be able to start up n instances of the program, where n is the number of cores you have, and the OS will take care of using all the cores for you.

In the best case it would run in 1/n the time, but this kind of thing can be tricky to get exactly right as some portions of the system, like memory, need to be shared between the processes and contention between processes can cause things not to scale linearly. If the split is easy to do I'd give it a try. You can also just try running the same program twice and see how long it takes to run, if it takes the same amount of time to run one as it does to run two you're likely all set, just split your data and go for it.

Trying jruby and some threads would probably help, but that adds a fair amount of complexity. (It would probably be a good excuse to learn about threading.)

Making ruby program run on all processors

Update

Update #2

4 Answers4