On Fri, 2013-06-07 at 17:02 +0800, tiejun.chen wrote: > On 06/07/2013 04:53 PM, Benjamin Herrenschmidt wrote: > > On Fri, 2013-06-07 at 15:46 +0800, tiejun.chen wrote: > >> On 06/07/2013 03:41 PM, Benjamin Herrenschmidt wrote: > >>> Another question... > >>> > >>> Do you guys happen to have a patch to emulate fsqrt in the kernel ? > >> > >> Seems this is already emulated: > >> > >> arch/powerpc/math-emu/fsqrt.c > >> > >> You can enable CONFIG_MATH_EMULATION to try. > > > > Is math emu expected to work at all on top of a real FPU ? I though it > > didn't ... maybe I'm wrong. > > As I understand often the real FPU can't support all float instructions, so > we > have to enable this to emulate those unsupported float instructions in that > scenario.
Ok, two things come to mind here: - do_mathemu doesn't do giveup_fpu() so the FPU state might still be in the "live" FP registers and not in the thread_struct, so it can't work... unless I missed something. - mathemu uses solely integers. For something like fsqrt it's going to suck a lot more than implementing using floating points in the kernel. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list [email protected] https://lists.ozlabs.org/listinfo/linuxppc-dev
