Re: Question on BIGGEST_ALIGNMENT in GCC on NetBSD/m68k

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

On Wed, 2025-06-11 at 18:32 +0300, Eero Tamminen wrote:
> It will decrease performance if increased alignment means that something 
> that fit earlier into i/d-cache, does not fit any more.

»Control whether GCC aligns int, long, long long, float, double, and long double
 variables on a 32-bit boundary (-malign-int) or a 16-bit boundary (-mno-align-int).
 Aligning variables on 32-bit boundaries produces code that runs somewhat faster on
 processors with 32-bit busses at the expense of more memory.«

Source: https://gcc.gnu.org/onlinedocs/gcc-3.1.1/gcc/M680x0-Options.html

> (68030 has 256 bytes, 68040 has 4 KB, and 68060 has 8 KB, of both.)
> 
> To get some numbers on this...
> 
> if you could provide vmlinuz & System.map files for both (otherwise 
> identical) 2-byte & 4-byte alignment kernel builds, using kernel config 
> here:
> https://github.com/hatari/hatari/blob/main/tools/linux/kernel.config
> 
> I could measure the perf difference for the whole kernel boot, and if 
> there are differences, profile what causes those differences.

But anyway, as I have said before, I am not going to change my mind on this
and I'm already working on it. If you prefer maintaining a Linux port with
2 bytes alignment, you are free to do so. But please don't expect me to waste
my time on it.

Thanks,
Adrian

-- 
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