The rule of thumb is don't bother spawning more threads than you
have cpus. You're just wasting resources mostly.
You REALLY don't want more threads trying to run than you have cores.
Threads in a wait state, are less of an issue, but they still use up
resources.
Personally I'd never use more threads than cores as a program design,
but I'm a performance whore. ;)
Could you explain why you believe this a bit more? I'm curious because
I've worked with databases and the rule of thumb there was you should
configure them to use twice as many threads as number of cores/CPUs.
The reasoning, I believe, is that if one thread on the CPU is stalled,
another thread can execute in it's place. And yes, I believe this was
before hyperthreading.
Though I wasn't informed of the specifics as to why, I'm guessing it's
mainly because with a database, there's a good chance you have to
perform some sort of disk I/O. Therefore instead of having the CPU wait
while the I/O is occurring, another thread can start executing while the
original is waiting.
Casey
