Communications of the ACM
Why Desktop Multiprocessing Has Speed Limits
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Despite the mainstreaming of multicore processors for desktops, not every desktop application can be rewritten for multicore frameworks, which means some bottlenecks will persist. "If you have a task that cannot be parallelized and you are currently on a plateau of performance in a single-processor environment, you will not see that task getting significantly faster in the future," says analyst Tom Halfhill.
Adobe Systems' Russell Williams points out that performance does not scale linearly even with parallelization on account of memory bandwidth issues and delays dictated by interprocessor communications. Analyst Jim Turley says that, overall, consumer operating systems "don't do anything smart" with multicore architecture.
"We have to reinvent computing, and get away from the fundamental premises we inherited from von Neumann," says Microsoft technical fellow Burton Smith. "He assumed one instruction would be executed at a time, and we are no longer even maintaining the appearance of one instruction at a time."
Analyst Rob Enderle notes that most applications will operate on only a single core, which means that the benefits of a multicore architecture only come when multiple applications are run.
"What we'd all like is a magic compiler that takes yesterday's source code and spreads it across multiple cores, and that is just not happening," says Turley.
Despite the performance issues, vendors prefer multicore processors because they can facilitate a higher level of power efficiency. "Using multiple cores will let us get more performance while staying within the power envelope," says Acer's Glenn Jystad.
From Computerworld
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