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
