[Nauty] Squeezing out another 10%...

Brendan McKay bdm at cs.anu.edu.au
Mon Feb 14 18:30:02 EST 2005

* Gordon Royle <gordon at csse.uwa.edu.au> [050214 17:04]:
> I have discovered through experimentation that I get an additional 10% 
> performance out of geng (and hence presumably) nauty by altering the 
> optimization flags from the supplied defaults... I am using a Pentium 4 
> machine, and if I put
> 	gcc -O2 -Dmarch=pentium4

I guess you mean
      gcc -O2 -march=pentium4
Somehow the configuration file (configure.ac) misses this case.
Now it is included.

I use an athlon k7, but gcc 3.3.4 does not have -march=k7.  Using
-march=k6 gives worse performance than the default  -march=i686.
Trying to automatically select the best options is hard.

> then it is about 10% faster than
> 	gcc -O4
> Interestingly, it proves better to use O1/O2 with the 
> architecture-specific flag than to use O3 or higher...

That will probably depend on which exact chip you have (eg specs
of on-board cache) and will also vary from one program to another.


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