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    SubjectRe: page table lock patch V15 [0/7]: overview
    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.

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