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    SubjectRe: [ANNOUNCE] New utility: 'trace'
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    On Wed, 2010-11-17 at 14:10 +0100, Ingo Molnar wrote:
    > * Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > > On Wed, 2010-11-17 at 13:53 +0100, Frederic Weisbecker wrote:
    > > > On Wed, Nov 17, 2010 at 12:35:50PM +0100, Peter Zijlstra wrote:
    > > > > On Wed, 2010-11-17 at 09:30 +0100, Ingo Molnar wrote:
    > > > > > > For example I'm currently working with dozens of trace_printk() and I would be
    > > > > > > very happy to turn some of them off half of the time.
    > > > > >
    > > > > > I guess we could try such a patch. If you send a prototype i'd be interested in
    > > > > > testing it out.
    > > > >
    > > > > I don't see the point, the kernel shouldn't contain any trace_printk()s
    > > > > to begin with..
    > > >
    > > >
    > > > It's oriented toward developers. Those who use dozens of tracepoints in
    > > > their tree because they are debugging something or developing a new feature,
    > > > they might to deactivate/reactivate some of these independant points.
    > > >
    > > > This can also apply to dynamic_printk of course.
    > > >
    > > > Well, the very first and main point is to standardize trace_printk into
    > > > a trace event so that it gets usable by perf tools. I have been asked many
    > > > times "how to use trace_printk() with perf?".
    > >
    > > Thing is, since its these dev who add the trace_printk()s to begin with, I don't
    > > see the point in splitting them out, if you didn't want them why did you add them
    > > to begin with?!
    >
    > That's a common workflow: lots of printks (trace_printk's) put all around the code -
    > and sometimes one set of tracepoints is needed, one time another set.
    >
    > _If_ we succeed in presenting them like Frederic suggested it, and if we make the
    > turning on/off _simpler_ (no kernel modification) and faster (no kernel reboot) via
    > the tooling, people like Frederic might start using it.
    >
    > I dont think we should fight the workflow itself - it makes sense.
    >
    > The only question is whether we can represent it all in a nicer fashion than 'modify
    > the source code and reboot'. If we cannot then there's no point - but i'm not sure
    > about it and Frederic seems to be convinced too that he can make such a switch
    > on/off facility intuitive. We'll only see if we try it.
    >
    > Also, i dont see any harm - do you?

    Yes, trace_printk() is a pure debug interface, solely meant for the edit
    + reboot cycle.

    If you want anything more than that we've got tracepoints. The rule up
    until now has been to never merge a trace_printk() user.


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