Messages in this thread | | | Subject | Re: [PATCH/RFC] Math-emu kills the kernel on Athlon64 X2 II -- it's terminally broken | From | Alan Cox <> | Date | Tue, 03 Oct 2006 12:53:34 +0100 |
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Ar Maw, 2006-10-03 am 12:11 +0200, ysgrifennodd Andi Kleen: > On Tuesday 03 October 2006 05:24, Randy Dunlap wrote: > > Actually I looked at the code more closely. It looks like kernel math > emulation is much more broken. e.g. kernel_fpu_begin() is missing > code and lots of other paths in i387 that need to check HAVE_HWFP don't.
That check would be wrong anyway. A kernel built with FPU emulation boots, runs and uses the hardware FPU code correctly. The problem area is the X86_FEATURE_foo stuff. I think that comes down to a single thing - if we have FPU disabled clear X86_FEATURE_FXSR|X86_FEATURE_MMX| X86_FEATURE_SSE* in the boot cpu features during early option parsing/setup. Basically the emulated FPU is forgetting to tell the truth about the fact its a very basic FPU.
Alan
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