Re: Latest sources from CVS.

[Thiemo Seufer <ica2_ts@csv.ica.uni-stuttgart.de>]

Ralf Baechle wrote:
> On Fri, Dec 06, 2002 at 06:18:22PM +0000, Dominic Sweetman wrote:
> 
> > > The first kernel was built as 64-bit ELF using 64-bit pointer and 
> > > everything
> > > 64-bit.  The second kernel was built using the -Wa,-32 trick.  That's over
> > > 12% of bloat for full 64-bitiness which brings zero gain.
> > 
> > Percentages are dangerous things.  This is 220Kbytes of memory, which
> > currently represents an investment of about $0.05.  There may be
> > embedded linux applications which care about 5c cost, but they
> > probably won't use any variety of 64 bits...
> 
> I'd worry less if that was just 220kB of unused memory wasted.  But it's
> actually inflated code, it's wasted i-cache and cycles.  220kB translates
> to alost 7 times the size of today's typical 32kB i-cache.
> 
> Even if Thiemo was right this trick is probably the biggest micro-
> optimization of the decade ...

Even if it was such a big win it would IMHO be better to use N64 and
teach the assembler some optimization for such register loads.
-Wa,--sign-extend-immediates shouldn't be that complicated to implement.


Thiemo