make -j optimization

[Brendan]

On Thursday 30 September 2004 13:42, David Kramer wrote:
> In GNU make, you can specify a -j <n> option, to run <n> commands
> simultaneously.  This is good.
>
> I'm having an argument with a coworker over whether specifying a value for
> <n> greater than the number of the processors in the system actually does
> any good or not.  I don't see how it can.  In fact, specifying one fewer
> than the number of processors shoudl have almost the same performance as
> specifying the number of processors.

I'm sure other know much more than I do, but with 2 processors, we always used 
-j3, because if one thread is waiting for something (input, i/o, whatever) 
then the 3rd process comes in and balances it back out.

There are loads of benchmarks on this, so googling might be your best bet.