Testing performance of parallel programs on a single core machine

Question

I would like to start playing with concurrency in the programs I write (mostly for fun), but I don't own a multi-core system and can't afford one any time soon. I run linux. Is there a way to, for example with a Virtual Machine, compare the performance of a multi-threaded implementation of a program with a single-threaded version, without actually running it on hardware with multiple processors or cores?

That is, I would like to be able to implement parallel algorithms and be able to say that, yes, this multithreaded implementation is better-performing than the single-threaded.

Thanks

Answer 1

If you have only one core/cpu and your algorithm is cpu intensive, you will probably see multi-threaded program is actually slower than the single-threaded one. But if you have program use i/o in one thread and cpu in another for example, then you can see the multi-threaded program is faster.

Answer 2

To observe effects other than potentially improved locality, you'll need hardware or a simulator that actually models the communication/interaction that occurs when the program runs in parallel. There's no magic to be had.

Answer 3

Depending on what you're benchmarking you might be able to use an Amazon EC2 node. It's not free, but it's cheaper than buying a computer.

Answer 4

You can not test multithreaded programs reliably on a single core machine. Race conditions will show up very differently or even be totally hidden on a single core machine. The performance will decrease etc.

If you want to LEARN how to program multiple threads, you can do so on a single core machine for the first steps (i.e how works the API etc.). But you'll have to test on a multicore machine and its very likely that you will see faults on a multicore machine that you dont see on a single core machine.

Virtual machines are by my experience no help with this. They introduce new bugs, that didnt show up before, but they CANT simulate real concurrency with multiple cores.