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    SubjectRe: Oprofile : need to adjust PC by 16 bytes
    Mikael Pettersson a écrit :
    > Eric Dumazet writes:
    > > Very strange results on my Intel E5450 CPU
    > >
    > > I found that I have to bias regs->ip by 16 bytes in order to have
    > > correct profiling.
    > >
    > > Does it rings a bell to anyone ?
    >
    > The term is "skid". All OO processors are susceptible to it,
    > as was known already to the Alpha "continous profiling"
    > performance counter folks.

    Cool. Maybe this can explain the other bug I have with oprofile.

    >
    > And no, blindly subtracting 16 from IP is not a fix.

    Who mentioned a fix ? I am only giving more fuel to Intel guys so they
    hopefully can give us a working oprofile.


    >
    > >
    > > opcontrol --version
    > > opcontrol: oprofile 0.9.4 compiled on Nov 3 2008 06:45:57
    > >
    > > Thank you
    > >
    > > diff --git a/arch/x86/oprofile/op_model_ppro.c b/arch/x86/oprofile/op_model_ppro.c
    > > index 3f1b81a..051fb16 100644
    > > --- a/arch/x86/oprofile/op_model_ppro.c
    > > +++ b/arch/x86/oprofile/op_model_ppro.c
    > > @@ -131,7 +131,9 @@ static int ppro_check_ctrs(struct pt_regs * const regs,
    > > continue;
    > > rdmsrl(msrs->counters[i].addr, val);
    > > if (CTR_OVERFLOWED(val)) {
    > > + regs->ip -= 0x10;
    > > oprofile_add_sample(regs, i);
    > > + regs->ip += 0x10;
    > > wrmsrl(msrs->counters[i].addr, -reset_value[i]);
    > > }
    > > }
    > >
    > > --


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