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    SubjectRe: [patch 10/10] Scheduler profiling - Use immediate values
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    Adrian Bunk <bunk@stusta.de> writes:

    > [...]
    > profiling = debugging of performance problems

    Indeed.

    > My words were perhaps a bit sloppy, but profiling isn't part of
    > normal operation and if people use a separate kernel for such
    > purposes we don't need infrastructure for reducing performance
    > penalties of enabled debug options.

    Things are not so simple. One might not know that one has a
    performance problem until one tries some analysis tools. Rebooting
    into different kernels just to investigate does not work generally:
    the erroneous phenomenon may have been short lived; the debug kernel,
    being "only" for debugging, may not be well tested => sufficiently
    trustworthy.

    Your question asking for an actual performance impact of dormant hooks
    is OTOH entirely legitimate. It clearly depends on the placement of
    those hooks and thus their encounter rate, more so than their
    underlying technology (markers with whatever optimizations). If the
    cost is small enough, you will likely find that people will be willing
    to pay a small fraction of average performance, in order to eke out
    large gains when finding occasional e.g. algorithmic bugs.

    - FChE
    -
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