Which number of processes will give me the best performance?

I am doing some expensive caluation开发者_运维问答s right now. It is one programm, which I run several instances of at the same time. I am running them under linux on a machine with 4 cpus with 6 cores each. The cpus are Intel Xeon X5660, which support hyper thearting. (That's some insane hardware, huh?) Right now I am running 24 processes at once. Would it be better to run more, b/c of HT ?

Don't think, measure

update

How long is a piece of string?

Measuring first is a good idea, but you can also consider following:

• If the processes may block (particulary on IO), more of them is probably better.
• If the processes do a lot of math most of their time, you may take advantage of HyperThreading with more processes.
• On the other hand, if the processes have any shared state (memory or files), too much of them will increase contention and cache thrashing.

Without more information on your calculations it's going to be difficult, if not impossible, to give you a definitive answer. Even with this information there's a good chance any answer would be a guess.

You really need to do some timings/profiling of your solution. However, in the first instance you need to be able to configure the number of threads/processes you run at any one time.

Once you have this you can set up a scenario, run it and measure the result.

Repeat for different values and see which performs best.

I was about to type almost exactly what Viktor wrote, so I have him +1 instead.

I would like to add that processes impose more overhead when there is a context switch than threads.

If your application architecture allows it, consider a single process with multiple threads or perhaps N processes with M threads each, where N and M are determined by benchmarking.