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    SubjectRe: [patch 4/4] KVM-trace port to tracepoints
    On Wed, 2008-07-23 at 11:08 +0300, Avi Kivity wrote:
    > Peter Zijlstra wrote:
    > > On Tue, 2008-07-22 at 21:46 +0300, Avi Kivity wrote:
    > >
    > >> Jan Kiszka wrote:
    > >>
    > >>> That's true - as long as you don't have to add/remove/modify
    > >>> tracepoints. I had to do this job in the past (not for KVM). Having 1
    > >>> spot in 1 file (based on generic probes) would be handier in that case
    > >>> than 5 spots in 3 files. But if the KVM tracepoints are considered
    > >>> stable in their number and structure, that shouldn't be an issue here.
    > >>>
    > >>>
    > >>>
    > >> Tracepoints aren't stable; they are artefacts of the implementation.
    > >>
    > >
    > > Which IMHO makes it unsuitable for trace_mark() as that will be exported
    > > to user-space, and every time you change your tracepoints you'll change
    > > user visible things - not nice.
    > >
    > They are used for debugging (mostly performance related), so changes are
    > expected.
    > What uses of trace_mark() depend on a stable interface? blktrace?

    There are currently no trace_mark() sites in the kernel that I'm aware
    of (except for the scheduler :-/, and those should be converted to
    tracepoints ASAP).

    Andrew raised the whole point about trace_mark() generating an
    user-visible interface and thus it should be stable, and I agree with

    What that means is that trace_mark() can only be used for really stable

    This in turn means we might as well use trace points.

    Which allows for the conclusion that trace_mark() is not needed and
    could be removed from the kernel.

    However - it might be handy for ad-hoc debugging purposes that never see
    the light of day (linus' git tree in this case). So on those grounds one
    could argue against removing trace_mark.

     \ /
      Last update: 2008-07-23 10:57    [W:0.020 / U:7.660 seconds]
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