Re: [MiNT] Some mintlib patches

[Vincent Rivière <vincent.riviere@freesbee.fr>]

Hello.

> I agree with you on this after all, maybe there's really m68020-60 vs 
> m68060 difference out of question. However, I have one experience where 
> at least 68000 vs m680[20-]60 had not some but DRASTIC effect -- and 
> that was gcc.

First of all, I know only the ST hardware... I know nearly nothing about 
Falcon, 68030 and FPU... So don't blame me too much.

I don't know if GCC makes a big difference between -m68020-60 and 
-m68060. In order to know it, we have to make a realistic benchmark with 
a C program which runs slow, without any hand-written assembly code. 
Archivers usually use only integers, and are slow with big files (even 
on a ramdisk). Good candidates may be gzip, bzip2, infozip... For the 
FPU, it may be harder to compare, because it relies on the quality of 
the libm, and its respect of the different CPU options. Some math 
intensive program, like POV-Ray, could be a good benchmark.

Another very important parameter is alignment. As discussed here not 
long ago, aligning the longs on multiples of 4 does matter in the 
FastRAM, and I believe it could make a big difference. Because the 
current GCC doesn't try to align the longs, their alignment is just 
random ! So any benchmark with randomly aligned longs will produce 
random results.

So before benchmarking, we must align the longs.
It may not be so difficult. The kernel could stay unaligned, because it 
stays in memory, so its speed will remain the same between all tests.
Care must be taken to keep unchanged the structures shared by the kernel 
and the MiNTLib to not break the kernel binary compatibility. Any other 
structure can be realigned, as long as every library using it is 
recompiled, too. We have to ensure the stack is always long aligned, as 
well as malloc(), and that's all

After that, another interesting test would be to do the benchmark with 
different PRG flags (using FastRAM or not).

Anyway, some benchmarking may be interesting even without alignment...

--
Vincent Rivière