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    SubjectRe: [patch-early-RFC 00/10] LTTng architecture dependent instrumentation

    hi Mathieu,

    * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:

    > Hi,
    >
    > Here is the architecture dependent instrumentation for LTTng. [...]

    A fundamental observation about markers, and i raised this point many
    many months ago already, so it might sound repetitive, but i'm unsure
    wether it's addressed. Documentation/markers.txt still says:

    | * Purpose of markers
    |
    | A marker placed in code provides a hook to call a function (probe)
    | that you can provide at runtime. A marker can be "on" (a probe is
    | connected to it) or "off" (no probe is attached). When a marker is
    | "off" it has no effect, except for adding a tiny time penalty
    | (checking a condition for a branch) and space penalty (adding a few
    | bytes for the function call at the end of the instrumented function
    | and adds a data structure in a separate section).

    could you please eliminate the checking of the flag, and insert a pure
    NOP sequence by default (no extra branches), which is then patched in
    with a function call instruction sequence, when the trace point is
    turned on? (on architectures that have code patching infrastructure -
    such as x86)

    Ingo


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