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    SubjectRe: Memory Barrier Definitions
    Dave Engebretsen wrote:
    > wrote:
    > >
    > > On Tue, 2002-05-07 at 16:27, Alan Cox wrote:
    > > > and our current heirarchy is a little bit more squashed than that. I'd
    > > > agree. We actually hit a corner case of this on the IDT winchip x86 where
    > > > we run relaxed store ordering and have to define wmb() as a locked add of
    > > > zero to the top of stack - which does have a penalty that isnt needed
    > > > for CPU ordering.
    > > >
    > > > How much of this impacts Mips64 ?
    > >
    > > In terms of the MIPS{32|64} ISA, the current primitives seem fine;
    > > there's only 1 option defined in the ISA: 'sync'. Order for all
    > > off-cache accesses is guaranteed around a sync.
    > >
    > > It gets a bit more complicated when you talk about what particular
    > > implementations do, and ordering rules for uncached vs cached accesses,
    > > but to the best of my knowledge there aren't any fundamental problems as
    > > described for the PPC.
    > >
    > > -Justin

    I am curious what the definition of memory barriers is for IA64, Sparc,
    and x86-64.

    From what I can tell, sparc and x86-64 are like alpha and map directly
    to the existing mb, wmb, and rmb semantics, incluing ordering between
    system memory and I/O space. Is that an accurate assesment?

    IA64 has both the mf and mf.a instructions, one for system memory the
    other for I/O space. What is required for ordering of references
    between the spaces? That is not clear to me looking at the ia64

    Thanks for any input -

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