Author: Robert Hyatt
Date: 15:33:49 07/22/03
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On July 22, 2003 at 16:53:18, J. Wesley Cleveland wrote: >On July 22, 2003 at 16:09:51, Robert Hyatt wrote: > >> >> >>In looking at your code, it should be noted that a _good_ compiler will >>eliminate it completely, which is a problem. IE a good compiler builds a >>complete dependency graph, and it will notice that you are not using any >>of the results computed, and they should be simply dropped as "dead code". >> >>I'll test this with gcc and icc and see what happens, for fun. > >I use MSVC. Since the results were significantly different, I had a clue that my >code was doing something. If you aren't careful, you can run the _same_ executable N times and get N different speeds. A program can be scattered around in physical memory in different ways that cause different cache line aliasing conflicts. That is one way to see a 1% speed change. Go to a WMCCC event and watch guys test, reboot, test, etc until they get a memory layout they like (which produces the highest NPS they can reach) and then they run as is without re- starting the program to keep that optimal layout.
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