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    SubjectRe: [PATCH 01/22] x86: add methods for writing of an MSR on several CPUs
    On Thu, May 21, 2009 at 07:21:21AM -0700, H. Peter Anvin wrote:
    > Borislav Petkov wrote:
    > >>>
    > >> smp_call_function_many() does allow concurrent execution.
    > >
    > > Well, IMHO, not an absolutely concurrent execution since you can't
    > > control at what moment in time the IPIs will be executed on each core,
    > > IOW, the respective call function IPIs will generally not coincide on
    > > each core at a given moment in time. This is especially true if you're
    > > sending IPIs to cores across nodes.
    > >
    > > And there's hypothetically a small window where you might get an
    > > inconsistent MSR content across cores. It's a whole another question
    > > whether this is going to be relevant.
    > >
    > It *allows* concurrent execution. It doesn't *guarantee* concurrent
    > execution.

    Exactly what I'm trying to say.

    > > So, the actual question is do we need that done in msr.c? If there are
    > > no potential users, I could easily do the whole thing in the driver and
    > > do not touch x86 code.
    > Only if we care about the additional performance of having it be
    > nonserializing.

    Well, let's do the nonserializing thing and have it done right from the
    beginning. We might not care now but who knows..?


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