Re: [Devel] Question about optimizing FT_MulFix.

[David Turner]

Hi Nathan,

> 
> On a 400MHz G4:
> address@hidden:~/timecpu$ gcc -O6 fixmul64.c test_fixmul.c
> address@hidden:~/timecpu$ ./a.out
> mult_fix1 : time = 6.63000
> mult_fix2 : time = 5.43000
> mult_fix3 : time = 6.22000
> mult_fix4 : time = 7.44000
> mult_fix5 : time = 6.42000
> address@hidden:~/timecpu$ cat /proc/cpuinfo
> cpu             : 7400 (G4)
> clock           : 400MHz
> bogomips        : 796.76
> L2 cache        : 1024K unified
> memory          : 128MB
> 
> On a 400MHz G3:
> bash-2.05$ gcc -O6 fixmul64.c test_fixmul.c
> bash-2.05$ ./a.out
> mult_fix1 : time = 6.65000
> mult_fix2 : time = 5.44000
> mult_fix3 : time = 6.25000
> mult_fix4 : time = 7.45000
> mult_fix5 : time = 6.45000
> bash-2.05$ cat /proc/cpuinfo
> cpu             : 740/750
> clock           : 400MHz
> bogomips        : 798.40
> L2 cache        : 1024K unified
> memory          : 256MB
> 
> Dual G4 400MHz:
> address@hidden:~/timecpu$ gcc -O6 fixmul64.c test_fixmul.c
> address@hidden:~/timecpu$ ./a.out
> mult_fix1 : time = 5.93000
> mult_fix2 : time = 4.83000
> mult_fix3 : time = 5.55000
> mult_fix4 : time = 6.65000
> mult_fix5 : time = 5.83000
> 
> Which just proves that benchmarks are meaningless.
>
I wouldn't go that far ;-)

However, I'd certainly say that it proves that the benefits
of so-called "optimization" of C programs based on processor
heuristics aren't always real !!

Thanks a lot for your input,

Cheers,

- David