Nope. He just doesn't know anything about scheduling (or threading).
Moving a thread to a different processor is almost always a loss in
the real world (ie except for very long-lived threads with one thread
per proc on an otherwise idle box), because it means that not only do
you have the cost of migrating the process to the other processor, but
you lose cache-affinity (you need to save and restore as much context
as seperate processes whereas if they share a processor, all the
process data is in the processor cache for all threads to share
without cache misses). It also means that other processes suffer,
because your one multi-threaded process (in the case of 2-way SMP)
would get twice as many context switches (each thread would need to
get swapped in and out seperately per processor), and introduces lots
of luvverly atomicity nasties, because process data (visible to all
threads) needs to be available to all processors. Summary: Ouch.
The benefit of threading comes from the fact that things can be done
while parts of your process are blocked waiting for other things to
happen. You can do processing while blocked on a socket waiting for
connections for example. Remember also that your process is
constantly being scheduled on a processor and dropped. Multi-threaded
processes have "more bites of the cherry" when it comes to scheduling,
even on UP.
He would do well to remember the words of Dan Bernstein: "Don't
speculate- benchmark".
Sean
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