[Python-Dev] Dictionary sparseness (original) (raw)

Tim Peters tim.one@comcast.net
Mon, 05 May 2003 13:54:41 -0400

[Alex Martelli]

... As CPUs and floating-point units became fast enough, more and more of the speed issues with so-called "CPU intensive" bottlenecks in mechanical-engineering CAD actually became related to memory-access patterns (a phenomenon I had already observed when I worked on IBM multi-CPU mainframes with vector-units, being sold as "supercomputers" but in fact still having complex and deep memory hierarchies -- Cray guys of the time such as Tim no doubt had it easier!-).

Indeed, Seymour Cray used to say a supercomputer is a machine that transforms a CPU-bound program into an I/0-bound program, and didn't want anything "in between" complicating that view. As a result, optimizing programs to run on Crays was, while still arbitrarily difficult, generally a monotonic process, rarely beset by "mysterious regressions" along the way.

Now that gigabyte+ RAM boxes are becoming common, I wonder when someone will figure out that the VM machinery is just slowing them down <0.9 wink>.