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SubjectRe: [RFC][PATCH 0/2] tracing: Have trace_printk()s in the events/ directory
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On Thu, 2010-11-18 at 07:06 -0500, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@goodmis.org) wrote:
> > On Thu, 2010-11-18 at 11:41 +0100, Peter Zijlstra wrote:
> > > On Wed, 2010-11-17 at 22:58 -0500, Steven Rostedt wrote:
> > > > For example, I added a trace_printk() in kernel/sched.c at line 2180
> > > > and it creates:
> > > >
> > > > # ls /debug/tracing/events/printk/kernel/sched.c/2180/
> > > > enable format
> > > >
> > > > The format is the printk format:
> > > >
> > > > # cat /debug/tracing/events/printk/kernel/sched.c/2180/format
> > > > "migrate task %s:%d"
> > >
> > > *groan*, so you're creating a tracepoint per instance?
> > >
> > > That's going to be massive pain for perf.. I really don't see the point
> > > in splitting all that out.
> >
> > a) The file directory was what was asked about in the referenced email.
> > b) This is just an example of a way to display it to the user, which
> > seems to be very intuitive.
> > c) Perf can implement the details anyway it wants. It can make a single
> > tracepoint callback and have the enabling of the points as a special
> > filter.
> > d) This was just an RFC that Frederic asked if I would do. I thought it
> > would be a fun challenge and did it. Let it bit rot in hell for all I
> > care, I wasn't taking it any further anyway.
>
> Hi Steven,
>
> The LTTng tree still keeps the "trace_mark()" kernel markers, which are
> very very similar to ftrace_printk(). I'd be happy to combine the two
> eventually. This one file per line approach seems very good -- rather than
> explicitely naming each instance, as I did in trace_mark(), you end up
> automatically naming them by file/line number.
>
> How does this behave from within static inlines called multiple times and
> unrolled loops ?

Actually you mean macros:

You'll get a 2181-1, 2181-2, 2181-3, etc.

Although a trace_printk() in a header static inline may be interesting.

-- Steve




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