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    SubjectRe: [Perfctr-devel] Re: Enabling RDPMC in user space by default
    Andi Kleen wrote:
    > I think it's also a useful convention - RDTSC is becomming more and more
    > useless and you cannot expect user applications who just want to
    > measure some cycles to rely on ever changing instable or non existing
    > performance counter APIs.

    Users are even more unhappy with ever-changing ABIs -- such as the
    kernel taking away RDTSC.

    RDTSC+perfctr [Pettersson] still is the fastest way for user-mode code
    to count something that is highly correlated with both "billable"
    CPU time and "code quality" for a fixed task. With a little care
    RDTSC is close enough to monotonic that I find it very useful.
    Please don't take away user-mode RDTSC.

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