linux-kernel - Re: Nested events with zero deltas, can use absolute timestamps instead?

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Date:   Fri, 24 May 2019 08:48:44 -0700
From:   Jason Behmer <jbehmer@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     tom.zanussi@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: Nested events with zero deltas, can use absolute timestamps instead?

On Fri, May 24, 2019 at 8:25 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Fri, 24 May 2019 08:11:12 -0700
> Jason Behmer <jbehmer@...gle.com> wrote:
>
> > > > What do you think of that?
> > >
> > > I don't think that's confusing if its well documented. Have the user
> > > flag called "force_absolute_timestamps", that way it's not something
> > > that the user will think that we wont have absolute timestamps if it is
> > > zero. Have the documentation say:
> > >
> > >  Various utilities within the tracing system require that the ring
> > >  buffer uses absolute timestamps. But you may force the ring buffer to
> > >  always use it, which will give you unique timings with nested tracing
> > >  at the cost of more usage in the ring buffer.
> > >
> > > -- Steve
> >
> > Ah, I was thinking of doing this within the existing timestamp_mode
> > config file.  Having a separate file does make it much less confusing.
>
> Not a separate file, but a new tracing option.
>
> -- Steve

Sorry, I'm not sure I follow.  By new tracing option do you mean a new
option in the timestamp_mode file?  I guess in that case would that
still be the only writable option?  You could write 1/0 to the file
which would turn on/off force_absolute_timestamps, and reading the
file would show which of absolute, delta, and force_absolute was set?
Or did you mean something else by tracing option?