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    SubjectRe: [RFC PATCH 1/3] Unified trace buffer


    On Thu, 25 Sep 2008, Steven Rostedt wrote:
    >
    > Slight correction. You can annotate the function with "notrace" and
    > that function will not be traced. So the "only be disabled on a per-file
    > basis" statement is false.

    Ok. It's still true that we absolutely don't want to add random notrace
    markers to code just because it's shared with the scheduler. And
    "sched_clock()" is not a single function with just a few well-defined
    places, nor are all versions of it at all appropriate for tracing (the
    non-TSC ones are a total joke - it works for scheduling, but not tracing.
    Same goes for the virtualized versions).

    > Currently my code calls "ring_buffer_time_stamp" to get the time stamp,
    > whatever it will be. Currently it is using sched_clock, but since I have
    > it as a wrapper, it shouldn't be too hard to modify later.

    Yes. The code looked fine, and had a FIXME. I have no objection to using
    it as a known buggy approximation for TSC in order to not force every
    architecture to immediately write one when the patch is discussed. But I
    literally would expect that on x86, we'd basically just have a function
    that does "rdtsc" for the common case, along with possibly a generic
    fallback that does "xadd" in the absense of any other reasonable
    alternative.

    Linus


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