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    SubjectRe: [RFC perf,x86] P4 PMU early draft
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    On 2/10/10, Peter Zijlstra <peterz@infradead.org> wrote:
    > On Wed, 2010-02-10 at 13:38 +0300, Cyrill Gorcunov wrote:
    >> > I'd try BUG_ON(cpu != smp_processor_id()) and scrap passing that cpu
    >> > thing around.
    >> >
    >>
    >> no, i need cpu to find out if event has migrated from other thread and
    >> then i switch
    >> some thread dependant flags in hw::config (ie escr and cccr), or i
    >> miss something and events in one cpu just can't migrate to another
    >> cpu?
    >
    > Well, if we validate that cpu == smp_processor_id() (looking at
    > kernel/perf_event.c that does indeed seem true for
    > hw_perf_group_sched_in() -- which suggests we should simply remove that
    > cpu argument), and that cpu will stay constant throughout the whole
    > callchain (it does, its a local variable), we can remove it and
    > substitute smp_processor_id(), right?
    >

    yeah, seems so!

    > As to migration of the event, its tied to a task, we're now installing
    > the event for a task it wouldn't make sense to allow that to be
    > preemptible.
    >
    >

    ok, thanks for explanation, Peter! I'll take a closer look as only get
    back from office.


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