"A Fundamental Turn Toward Concurrency in Software"

Jp Calderone exarkun at divmod.com
Sat Jan 8 16:44:53 CET 2005


On Sat, 08 Jan 2005 14:22:30 GMT, Lee Harr <lee at example.com> wrote:
>>> [http://www.gotw.ca/publications/concurrency-ddj.htm]. It argues that the 
> >> continous CPU performance gain we've seen is finally over. And that future 
> >> gain would primary be in the area of software concurrency taking advantage 
> >> hyperthreading and multicore architectures.
> >>
> 
> > Well, yes. However, it's not as bad as it looks. I've spent a good part
> > of my professional life with multiprocessors (IBM mainframes) and
> > I have yet to write a multi-thread program for performance reasons.
> > All of those systems ran multiple programs, not single programs
> > that had to take advantage of the multiprocessor environment.
> > Your typical desktop is no different. My current system has 42
> > processes running, and I'd be willing to bet that the vast majority
> > of them aren't multi-threaded.
> >
> 
> Exactly. If every one of your processes had its own 2 Ghz processor
> running nothing else, I think you would be pretty happy. Your OS
> had better be well-written to deal with concurrent access to
> memory and disks, but I think for general application development
> there will be huge speed boosts with little need for new
> programming paradigms.

  Not likely.  How often do you run 4 processes that are all 
bottlenecked on CPU?  It's not a common usage pattern.  If you
have 16 CPUs, and 15 of them are running mostly idle processes
and that *one* process you'd wish would hurry the heck up and 
finish has the 16th pegged at 100% usage, you are not a happy 
camper.

  For the case where you do have a lot of competing unrelated 
processes, no doubt SMP is a big win automatically, but there 
will still need to be language innovations to make it easier 
to develop software which can benefit from the additional 
hardware for the more common case of individual CPU hungry 
processes.

  Jp



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