Messages in this thread | | | From | Jakub Jelinek <> | Subject | Re: floating-point abuse in 2.1.113 | Date | Tue, 4 Aug 1998 13:21:26 +0200 (MET DST) |
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> > On Tue, 4 Aug 1998, Mikael Pettersson wrote: > > > Right. Floating-point is banned within the Linux kernel, yet some > > Uh... Just a stupid question... Why floating-point is banned?
On most platforms (all but sparc64, I think), FPU regs are always owned by application, ie. there is no save/restore around traps. So you clutter up apps registers (the compiler of course does not generate any code to save it/restore it when entering a function using FPU, as it is call clobbered).
If you want, take a look at my latest sparc64 FPU saving/restoring code to see how complex is it to do it right and quickly. And even on sparc64, you cannot use FPU in normal code, unless you before call some asm and afterwards as well, so it is designed just for the high bandwidth VIS operations, like memcpy/memset/IP csum/xor_block.
Cheers, Jakub ___________________________________________________________________ Jakub Jelinek | jj@sunsite.mff.cuni.cz | http://sunsite.mff.cuni.cz Administrator of SunSITE Czech Republic, MFF, Charles University ___________________________________________________________________ Ultralinux - first 64bit OS to take full power of the UltraSparc Linux version 2.1.112 on a sparc64 machine (498.80 BogoMips). ___________________________________________________________________
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