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    SubjectRe: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods
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    On Mon, 2009-06-15 at 21:07 +0200, Ingo Molnar wrote:
    > * Ingo Molnar <mingo@elte.hu> wrote:
    >
    > > > To a point where it cannot afford a simple register save/restore
    > > > ?
    > > >
    > > > There is "caring" and "_caring_". I am tempted to ask what NMI
    > > > handler execution frequency you have in mind here to figure out
    > > > if we are not trying to optimize sub-nanoseconds per minutes. ;)
    > >
    > > I routinely run 'perf' with half a million NMIs per second or
    > > more. ( Why wait 10 seconds for a profile you can get in 1 second?
    > > ;-)
    > >
    > > Granted that is over multiple CPUs - but still performance does
    > > matter here too.
    > >
    > > Reading cr2 is certainly fast. Writing it - dunno.
    >
    > But one thing is sure: it is certainly going to be faster than the
    > INVLPG(s!) we have to do with the GUP solution.

    Sure, but we only pay that price when we do the callchain bit, not on
    every NMI.



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