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    SubjectRe: [PATCH -tip] x86,perf: P4 PMU -- protect sensible procedures from preemption
    On Thu, May 06, 2010 at 09:45:24AM -0400, Steven Rostedt wrote:
    ...
    > > > We want the one with the least runtime overhead. These are instrumentation
    > > > routines, so we want to optimize them as much as possible.
    >
    >
    > Yeah, my point was either disable preemption or keep the checks. In
    > other words, if you don't disable preemption, do not use
    > raw_smp_procesor_id(), because then we will not catch it if it changes
    > in the future.
    >
    > > ok, Ingo, dont apply this patch then for a while.
    >
    > Send another patch, I'll test it again ;-)
    >
    > -- Steve
    >
    >

    Ingo, Steven, it seems we have potential preemtion available
    in perf_event.c:validate_group:x86_pmu.schedule_events() which
    is reached via syscall from userspace perf_event_open() call,
    so get_cpu is still needed. But I'm a bit messed with call
    graph at the moment :(

    -- Cyrill


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