Messages in this thread | | | Date | Thu, 10 Jul 2008 13:28:32 -0700 | From | Randy Dunlap <> | Subject | Re: [PATCH] ftrace: Documentation |
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On Thu, 10 Jul 2008 21:59:01 +0200 Elias Oltmanns wrote:
> Steven Rostedt <rostedt@goodmis.org> wrote: > > This is the long awaited ftrace.txt. It explains in quite detail how to > > use ftrace and the various tracers. > > > > Signed-off-by: Steven Rostedt <srostedt@redhat.com> > > Exactly what I've just been looking for. Very nice. > > As I read through this enlightening peace, I took the liberty to make > some comments where I thought I'd spotted some mistake. Note that I'm > not a native English speaker nor familiar with all the terminology. > Also, I didn't exactly scratch my head when I had a bad feeling about > something but couldn't come up with a better idea straight away. > Basically, I just skimmed through the lines because im interested in the > matter. > > Anyway, here it goes:
[I'm dropping good comments, just making more comments.]
> > + set_ftrace_notrace: This has the opposite effect that > > + set_ftrace_filter has. Any function that is added > > + here will not be traced. If a function exists > > + in both set_ftrace_filter and set_ftrace_notrace > > (comma) > > > + the function will _not_ bet traced.
be
> > + stacktrace - This is one of the options that changes the trace itself. > > change
changes :) [subject is "This", singular]
> > > + When a trace is recorded, so is the stack of functions. > > + This allows for back traces of trace sites. > > + > > +sched_switch > > +------------ > > + > > +This tracer simply records schedule switches. Here's an example > > +on how to implement it.
of
> > use? > > [...] > > +Here we traced a 50 microsecond latency. But we also see all the > > +functions that were called during that time. Note that enabling > > by enabling? > > > +function tracing we endure an added overhead. This overhead may > > (comma) > > > +extend the latency times. But never the less, this trace has provided
nevertheless,
> > +some very helpful debugging. > > debugging information? > > > + > > + > > +preemptoff > > +---------- > > + > > +When preemption is disabled we may be able to receive interrupts but > > (comma) > > > +the task can not be preempted and a higher priority task must wait
cannot
> > +for preemption to be enabled again before it can preempt a lower > > +priority task. > > + > > +The preemptoff tracer traces the places that disables preemption. > > disable > > > +Like the irqsoff, it records the maximum latency that preemption > > +was disabled. The control of preemptoff is much like the irqsoff.
> > +Since this tracer only deals with RT tasks, we will run this slightly > > +different than we did with the previous tracers. Instead of performing
differently
> > +an 'ls' we will run 'sleep 1' under 'chrt' which changes the > > (comma) > > > +priority of the task.
> [...] > > +Where as the setting of the NEED_RESCHED bit happens on the
Whereas
> > +task's stack. But because we are in a hard interrupt, the test
^? That's not a complete sentence.
> > +is with the interrupts stack which has that to be false. We don't
interrupt > > ^^^^ > Superfluous that? Don't understand that sentence. > > > +see the 'N' until we switch back to the task's stack. > [...] > > +When dynamic ftrace is initialized, it calls kstop_machine to make it
^^ what is "it"?
> > +act like a uniprocessor so that it can freely modify code without > > +worrying about other processors executing that same code. At > > +initialization, the mcount calls are change to call a "record_ip" > > changed > > > +function. After this, the first time a kernel function is called, > > +it has the calling address saved in a hash table. > [...] > > +Two files that contain to the enabling and disabling of recorded > > +functions are: > > Can this be expressed somewhat differently?
or drop "to".
> > > + > > + set_ftrace_filter > > + > > +and > > + > > + set_ftrace_notrace > > + > > +A list of available functions that you can add to this files is listed > > these > > > +in: > > + > > + available_filter_functions > [...] > > +Perhaps this isn't enough. The filters also allow simple wild cards. > > +Only the following is currently available
Only the following are currently available:
> > + > > + <match>* - will match functions that begins with <match> > > begin > > > + *<match> - will match functions that end with <match> > > + *<match>* - will match functions that have <match> in it
--- ~Randy Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA http://linuxplumbersconf.org/
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