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    SubjectRe: [perfmon] Re: [perfmon2] perfmon2 merge news
    On Wed, Nov 14, 2007 at 06:13:42AM -0800, Stephane Eranian wrote:
    > > At least for x86 and I suspect some 1other architectures we don't
    > > initially need a syscall at all for this. There is an instruction
    > > RDPMC who can read a performance counter just fine. It is also much
    > > faster and generally preferable for the case where a process measures
    > > events about itself. In fact it is essential for one of the use cases
    > > I would like to see perfmon used (replacement of RDTSC for cycle
    > > counting)
    > >
    >
    > This only works when counting (not sampling) and only for self-monitoring.

    It works for global monitoring too.

    >
    > > Later a syscall might be needed with event multiplexing, but that seems
    > > more like a far away non essential feature.
    > >
    > On a machine with only two generic counters such as MIPS or Intel Core 2 Duo,
    > multiplexing offers some advantages. If NMI watchdog is enabled, then you drop
    > to one generic counter on on Core 2.

    NMI watchdog is off by default now.

    Yes longer term we might need multiplexing, but definitely not as first step.

    -Andi
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