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Full Discussion: Weird timing results in C
Top Forums Programming Weird timing results in C Post 302352644 by jim mcnamara on Saturday 12th of September 2009 01:54:05 PM
Old 09-12-2009
With regard to static functions:
I assume this is because the C99 standard says little about implemention of static text other than scope changes -

In large single file programs with a lot of static functions mixed in with auto functions -
I've encounteered really obscure problems in gcc 3.1, cc on HP UX 11.1. For example an auto function not being executed at all. Sounds odd, but it is true. The same "inherited program design" also screwed up optimizations by forcing the complier to make decisions it was not expected to make - according the HP compiler team anyway.

Basically to resolve the problems I had to completely turn off optimzation, and declare all functions static to get correct results. Since a fixed makefile was a requirement for the entire app suite, this meant a big rewrite for several very large programs.

Your problem is nothing like that. It almost HAS to be cache-related Based on what you said about your hardware, if you were to chunk your 125MB of data into 21 ~6MB chunks, then iterate (1,2,3) over each subset chunk the problem would not be there. If it is cache related - and with no other observations to work on that would be my guess.
 

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MAKE(1) 						      General Commands Manual							   MAKE(1)

NAME
make - a program for maintaining large programs SYNOPSIS
make [-f file] [-iknpqrst] [option] ... [target] OPTIONS
-f Use file as the makefile -i Ignore status returned by commands -k On error, skip to next command -n Report, but do not execute -p Print macros and targets -q Question up-to-dateness of target -r Rule inhibit; do not use default rules -s Silent mode -t Touch files instead of making them EXAMPLES
make kernel # Make kernel up to date make -n -f mfile # Tell what needs to be done DESCRIPTION
Make is a program that is normally used for developing large programs consisting of multiple files. It keeps track of which object files depend on which source and header files. When called, it does the minimum amount of recompilation to bring the target file up to date. The file dependencies are expected in makefile or Makefile , unless another file is specified with -f. Make has some default rules built in, for example, it knows how to make .s files from .c files. Here is a sample makefile . d=/user/ast # d is a macro program: head.s tail.s# program depends on these cc -o program head.s tail.s# tells how to make program echo Program done. # announce completion head.s: $d/def.h head.c # head.s depends on these tail.s: $d/var.h tail.c # tail.s depends on these A complete description of make would require too much space here. Many books on UNIX discuss make . Study the numerous Makefiles in the MINIX source tree for examples. SEE ALSO
cc(1). MAKE(1)
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