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    SubjectRe: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function_many())
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    On Wed, 2009-02-18 at 05:59 -0800, Nick Piggin wrote:
    > You're saying the problem is in generic_exec_single because I've
    > removed the smp_mb that inadvertently also serialises memory with
    > the x2apic on x86?

    yes.

    >
    > Indeed that could cause problems on some architectures which I
    > had hoped to avoid. So the patch is probably better off to first
    > add the smp_mb() to arch_send_call_function_xxx arch code, unless
    > it is immediately obvious or confirmed by arch maintainer that
    > such barrier is not required.

    For x2apic specific operations we should add the smp_mb() sequence. But
    we need to make sure that we don't end up doing it twice (once in
    generic code and another in arch code) for all the ipi paths.

    thanks,
    suresh



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