--- Nicolas Pitre nico@cam.org wrote:

On Wed, 25 Oct 2000, Andre wrote:

...

All results are in clock cycles on a Pentium III:

gcc version egcs-2.91.66 (ie stock RH 6.2):

gcc -O1 : 1329 clocks (asm mad_f_mul), 1529 clocks (C mad_f_mul) gcc -O2 : 1607 clocks (asm mad_f_mul), 2176 clocks (C mad_f_mul) gcc -O3 : 1608 clocks (asm mad_f_mul), 2186 clocks (C mad_f_mul)

gcc version 2.95.2 19991024:

gcc -O0 : 2946 clocks (asm mad_f_mul), 2616 clocks (C mad_f_mul) gcc -O1 : 1735 clocks (asm mad_f_mul), 1201 clocks (C mad_f_mul) gcc -O2 : 1380 clocks (asm mad_f_mul), 1567 clocks (C mad_f_mul) gcc -O3 : 1380 clocks (asm mad_f_mul), 1567 clocks (C mad_f_mul)

This is strange.

The gcc-2.95.2 results are somewhat different on a StrongARM. They are more inline with the egcs-2.91.66 results above...

In terms of clock cycles, I would expect a (single issue) StrongARM to require a lot more than a (super-scalar) Pentium III for a given C function.

Unfortunately though, I don't have a suitable ARM platform to do any gcc testing with, so haven't been able to test this. I have a copy of ARM's 'Armulator' simulator which gives very good profiling information, but only runs code compiled with ARM's C compiler. Unfortunately, ARM's C compiler makes such a bad job of 64bit data types that I don't think any MAD benchmarks generated this way are very useful as a guide to how fast the code would run when compiled with gcc.

I do have an ARM Integrator board (ARM720T cpu), which I guess should be able to run Linux, but I haven't yet investigated the effort required to get it to do so....

Out of interest, the imdct36() part of my ARM assembler imdct36 + windowing function requires just under 1100 clock cycles on the simulator. So with a bit of assembler tweaking, a humble StrongARM can be faster than a Pentium III :-)

Andre --

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