Richard B. Johnson wrote:
> On Mon, 3 Feb 2003, Martin J. Bligh wrote:
> 
>>People keep extolling the virtues of gcc 3.2 to me, which I'm
>>reluctant to switch to, since it compiles so much slower. But
>>it supposedly generates better code, so I thought I'd compile
>>the kernel with both and compare the results. This is gcc 2.95
>>and 3.2.1 from debian unstable on a 16-way NUMA-Q. The kernbench
>>tests still use 2.95 for the compile-time stuff.
>>
> 
> [SNIPPED tests...]
> 
> Don't let this get out, but egcs-2.91.66 compiled FFT code
> works about 50 percent of the speed of whatever M$ uses for
> Visual C++ Version 6.0

Interesting. I just noticed that I get 50% decrease in
the speed of my program if I just insert a printf(). I.E.
my program is like:

printf()
for(;;) {
     do_sorting_loop_test();
}

If I remove the initial printf it doubles in speed?
I assume this is some weird caching thing?
gcc is 3.2.1 (same happens for 2.95..)

<boggle>
Note this is with -O3. If I don't specify -O then
leaving the printf in speeds things up by about 15%
</boggle>

attached is the assembly for the slow and fast
in case anyone's interested.

Pádraig.