linux-kernel - RE: Tracing Requirements (was: [RFC/Requirements/Design] h/w error reporting)

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Date:	Wed, 10 Nov 2010 16:34:34 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	"bp@...en8.de" <bp@...en8.de>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mchehab@...hat.com" <mchehab@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: RE: Tracing Requirements (was: [RFC/Requirements/Design] h/w error
 reporting)

On Wed, 2010-11-10 at 16:06 -0500, Steven Rostedt wrote:

> > Perhaps you could explain the use cases of your "flight recorder",
> > because it seems that the name doesn't fit exactly, and this is
> > causing me (and maybe others) some confusion.

> 2) overwrite mode (flight recorder) - when the writer reaches the
> reader, it pushes the reader forward, and writes the new events over the
> old ones. This way, new events are always existent, where as old events
> are lost.

Ah, I forgot to mention use cases.

Even when recording a trace (lots of data, so it is saved to disk and
not all in kernel memory) I like to know that if something happens and
disables the trace, I have all the trace information up to the point of
failure.

With producer/consumer mode, you risk the reader being late and the
events in the trace that led up to failure (or any other anomaly) were
dropped.

-- Steve


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