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    SubjectRe: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic
    On Tue, 2009-06-16 at 10:13 +0200, Ingo Molnar wrote:

    > > By removing the types it becomes very difficult to verify the max
    > > depth. I really don't like removing them.
    > The fact that it implies an atomic section pretty much limits its
    > depth in practice, doesnt it?
    > All we need to track in the debug code is
    > max-{syscall,softirq,hardirq,nmi}. The sum of these 4 counts must be
    > smaller than the max - even if (as you are right to point out) we
    > dont hit that magic combo that truly maximizes the depth.

    Right, so the thing I'd worry about is someone adding kmap_atomic() to
    an interrupt context that didn't have interrupts disabled and then
    managing to nest that a few times.

    Suppose you put it in some IO completion handler, and someone has 4 IO
    controllers installed and all 4 IO interrupts come in at the 'same'

    With types you could warn on similarly to what we do today, but with the
    simple push/pop that might be a lot harder.

    Anyway, with the whole cr2 fiddling bit being discussed this seems to
    become redundant.

    > And note that in practice many of the current types are exclusive to
    > each other - so using the stack would _reduce_ the amount of
    > kmap-atomic space we need.

    Yeah, I did realize that.

     \ /
      Last update: 2009-06-17 09:47    [W:0.019 / U:125.264 seconds]
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