On Fri, Jan 14, 2005 at 09:08:54AM -0800, Christoph Lameter wrote: > On Fri, 14 Jan 2005, Andi Kleen wrote: > > > > Looked at arch/i386/lib/mmx.c. It avoids the mmx ops in an interrupt > > > context but the rest of the prep for mmx only saves the fpu state if its > > > in use. So that code would only be used rarely. The mmx 64 bit > > > instructions seem to be quite fast according to the manual. Double the > > > cycles than the 32 bit instructions on Pentium M (somewhat higher on Pentium 4). > > > > With all the other overhead (disabling exceptions, saving register etc.) > > will be likely slower. Also you would need fallback paths for CPUs > > without MMX but with PAE (like Ppro). You can benchmark > > it if you want, but I wouldn't be very optimistic. > > So the PentiumPro is a cpu with atomic 64 bit operations in a cmpxchg but > no instruction to do an atomic 64 bit store or load although the > architecture conceptually supports 64bit atomic stores and loads? Wild. It can do 64bit x87 FP loads/stores. But I doubt that is what you're looking for. -Andi - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.htmlReceived on Fri Jan 14 12:16:11 2005
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