Re: Newbie R5K questions -- -mips2 vs -mips4; is n32 ABI supported by Linux?

[Ralf Baechle <ralf@linux-mips.org>]

On Mon, Nov 17, 2003 at 02:04:26PM -0800, Jeffrey Baitis wrote:

> I'm currently trying to increase performance on our PMC-Sierra RM5231
> system by taking advantage of the MIPS IV ISA. This processor has a
> 32-bit address bus interface with 64-bit GPRs, so I guess that the
> choice of -mabi=n32 is ideal for this processor.

In addition to what Daniel just said ...

N32 requires a 64-bit kernel to run on which is significantly larger
thereby causing more cache misses so a 64-bit kernel is often slower.
On the kernel side a 64-bit kernel is drastically better at handling
large amounts of memory, so once a 32-bit kernel needs highmem the
64-bit kernel will win the race.  Often these effects influence
performance more than what you might gain from exploiting a new ISA.

  Ralf