Messages in this thread | | | Date | Thu, 6 Dec 2007 11:11:12 +0100 | From | Ingo Molnar <> | Subject | Re: [patch-early-RFC 00/10] LTTng architecture dependent instrumentation |
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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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