linux-kernel - Re: [PATCH 19/20 -v5] Trace irq disabled critical timings

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Message-ID: <Pine.LNX.4.58.0801231241090.13236@gandalf.stny.rr.com>
Date:	Wed, 23 Jan 2008 12:45:45 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Bird <tim.bird@...sony.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	John Stultz <johnstul@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 19/20 -v5] Trace irq disabled critical timings

On Wed, 23 Jan 2008, Frank Ch. Eigler wrote:
> On Wed, Jan 23, 2008 at 12:11:07PM -0500, Steven Rostedt wrote:
> > This patch adds latency tracing for critical timings
> > (how long interrupts are disabled for).
> > [...]
>
> Is there an opportunity here to share effort with latencytop, and
> ideally to use markers as much as possible for these event hooks?

Well, I just found out about latencytop a couple of days ago when Arjan
announced it. I took a quick look and it seems to be more of a general
collection of information. This tracer pinpoints out specific maxes.
Although I may be wrong (I have to admit, I haven't had the time to really
look at what LatencyTop does, but I have been using this tracer in -rt for
a number of years).

As for using markers, I just piggied back on top of lockdep, since it has
the same hooks that I needed. If we were to replace them with markers,
then I would say lockdep should use the markers too.

One thing about markers, only one probe may be allowed at a time. Perhaps
we should fix this by using something like I did with the mcount hook.

-- Steve

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