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Date: Mon, 22 Sep 2008 13:13:28 -0700
From: "Martin Bligh" <mbligh@google.com>
To: "Masami Hiramatsu" <mhiramat@redhat.com>
Subject: Re: Unified tracing buffer
Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
       "Linus Torvalds" <torvalds@linux-foundation.org>,
       "Thomas Gleixner" <tglx@linutronix.de>,
       "Mathieu Desnoyers" <compudj@krystal.dyndns.org>,
       "Steven Rostedt" <rostedt@goodmis.org>, od@novell.com,
       "Frank Ch. Eigler" <fche@redhat.com>,
       systemtap-ml <systemtap@sources.redhat.com>
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> I agree to integrate tracing buffer mechanism, but I don't think
> your proposal is the simplest one.
>
> To simplify, I think the layered buffering mechanism is desirable.
> - The lowest layer just provides named circular buffers(both per-cpu and
>  uni-buffer in system) and read/write scheme.
> - Next layer provides user/kernel interface including controls.
> - Top layer defines packet(and event) formatting utilities.
> - Additionally, it would better provide some library routines(timestamp,
>  event-id synchronize, and so on).
>
> Since this unified buffer is used from different kind of tracers/loggers,
> I don't think all of them(and future tracers) want to be tied down by
> "event-id"+"parameter" format.
> So, Sorry, I disagree about that the tracing buffer defines its *data format*,
> it's just overkill for me.

I think you're right that we can layer this, and we didn't make a particularly
good job of splitting those things out. I'll try to pull together
another revision
to reflect this and other suggested changes.

One thing that I think is still important is to have a unified timestamp
mechanism on everything, so we can co-ordinate different things back
together in userspace from different trace tools, so I intend to keep
that at a lower level, but I think you're right that the event id, etc can
move up into separate layers.