How do I make a multi-threaded app use all the cores on Ubuntu under VMWare?

Question

I have a multi-threaded C++ app (using pThreads) that processes a massive flat file that works great on Windows - uses all four cores on my puny CPU. Client wants to run the same code on Red Hat on a fire-breathing 64 Xeon CPU machine. So I compile it here (g++), ran it on Ubuntu on VMWare, and code only used one of the four cores. So I'm thinking that is a VMWare problem, and I send code to client - where it does the same thing (as far as I can tell remotely - mpstat -P ALL shows the CPUs barely loaded). Do I need to do something to force Red Hat to spread out the threads? Is there something I'm missing - I'm trying to get the "nice" priority changed next - but I feel like I'm missing something.

I can post code - but like I said, works great on Windows, uses pThreads, etc.

Answer 1

I would try to diagnose if this is a problem with your VM environment or your code. Here are some things to consider about your VM.

• Do you have vmware configured to allow access to multiple CPU's? I don't have experience with recent versions, but it used to be something you had to specifically allow. In VirtualBox, I have an option in the virtual machine configuration that states how many CPU's the guest is allowed to work with.

• If you cat /proc/cpuinfo from your Ubuntu guest do you see more than one CPU?

• Do you get proper use of multiple CPU's if you do something generic like going into your kernel source an running a kernel compile with make -j10?

If any of these things turn up wrong, they would indicate your VM is misconfigured rather than there being a problem with your code.