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

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Date:	Wed, 23 Jan 2008 13:48:39 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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:
> >
> > Also, the things the latency tracer and latecytop measure are quite
> > different. the latency tracer measures how long a non-schedulable
> > section is, latencytop measures how a task was scheduled away.
>
> The commonality I imagine is not in what sorts of reports they create,
> or where they complete the formatting for and end-user.  It is solely
> whether the kernel-side instrumentation sites can be represented by
> individual markers, so that these particular tools as well as future
> ones don't need to keep inserting custom code in similar or even the
> same places.

So basically just having the marker implementation there to let all
tracers access to irqs enabled/disabled.

One problem is that the hooks are alse in entry.S, so the tracing ends up
being architecture dependent. One solution is to have a "generic" hook for
trace_hardirqs_on/off (kind of like what I did here) and add a marker
inside that. The hooks in entry.S can call the generic function and have
the marker call the registered probes, be that lockdep, latencytap or
latency-trace.

Have the generic hook only be compiled in when one of the tracers or
lockdep is configured on and they select it.

-- Steve

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