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    SubjectRe: Cache coherency... and locking
    Date
    On Fri, 21 Jul 2000 12:57:21 +0200, 
    Manfred Spraul <manfred@colorfullife.com> wrote:
    >Keith Owens wrote:
    >> Linux requires strong write ordering[*]. That is, write A followed by
    >> write B will appear in memory in the order of A then B. So if any
    >> write on processor 1 is committed to memory then all preceding writes
    >> by processor 1 must already have been committed to memory.
    >>
    >Are you sure? Do you know a certain function that relies on strong write
    >ordering?

    I could not find an absolute statement of this requirement, just lots
    of mail about spinlock optimisation that assume strong write ordering.
    See http://www.uwsg.iu.edu/hypermail/linux/kernel/9911.3/0148.html
    where Linus says "Basically, everybody agrees on ordering of writes".
    It would be nice if the kernel gods made a definitive statement about
    the need or otherwise for strong write ordering.

    >Neither ia64 nor the other RISC processors guarantee strong write
    >ordering.

    IA64 load.acquire and store.release are available to do strong write
    ordering, although the default option is weak order.


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