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    SubjectRe: [PATCH] seqlock: serialize against writers


    On Fri, 29 Aug 2008, Gregory Haskins wrote:

    > Andi Kleen wrote:
    > >> Im running it on a x86_64 box as we speak. How can I tell if there is a
    > >> certain mode that is permitting this?
    > >>
    > >
    > > If the boot up says you're running with PMtimer then it uses the fallback
    > > (usually happens on pre Fam10h AMD boxes). A typical Intel box
    > > would use the faster ring 3 only TSC path and then explode with your
    > > change I bet.
    > >
    > > Or step with gdb through gettimeofday() and see if it does a syscall.
    > >
    > > -Andi
    > >
    >
    > It seems to be running fine with no indication it has fallen back.
    > Perhaps I need a certain workload to bring out the issue?

    Perhaps you never hit the slow path in userland. That's the only place it
    would write. Perhaps add a dummy static variable in the fast path, and
    write to it. See if that crashes you apps.

    -- Steve


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