linux-kernel - Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not set via debugfs

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Message-ID: <2020214533.2317.1394680887617.JavaMail.zimbra@efficios.com>
Date:	Thu, 13 Mar 2014 03:21:27 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Berg <johannes.berg@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	lttng-dev <lttng-dev@...ts.lttng.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not
 set via debugfs

----- Original Message -----
> From: "Andi Kleen" <andi@...stfloor.org>
> To: "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>
> Cc: "Andi Kleen" <andi@...stfloor.org>, "Steven Rostedt" <rostedt@...dmis.org>, "Frank Ch. Eigler" <fche@...hat.com>,
> linux-kernel@...r.kernel.org, "Ingo Molnar" <mingo@...nel.org>, "Frederic Weisbecker" <fweisbec@...il.com>, "Andrew
> Morton" <akpm@...ux-foundation.org>, "Johannes Berg" <johannes.berg@...el.com>, "Linus Torvalds"
> <torvalds@...ux-foundation.org>, "Peter Zijlstra" <peterz@...radead.org>, "Thomas Gleixner" <tglx@...utronix.de>,
> "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "lttng-dev" <lttng-dev@...ts.lttng.org>, "Rusty Russell"
> <rusty@...tcorp.com.au>
> Sent: Wednesday, March 12, 2014 11:15:01 PM
> Subject: Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not set via debugfs
> 
> On Wed, Mar 12, 2014 at 08:47:07PM +0000, Mathieu Desnoyers wrote:
> > ----- Original Message -----
> > > From: "Andi Kleen" <andi@...stfloor.org>
> > > To: "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>
> > > Cc: "Steven Rostedt" <rostedt@...dmis.org>, "Frank Ch. Eigler"
> > > <fche@...hat.com>, linux-kernel@...r.kernel.org, "Ingo
> > > Molnar" <mingo@...nel.org>, "Frederic Weisbecker" <fweisbec@...il.com>,
> > > "Andrew Morton" <akpm@...ux-foundation.org>,
> > > "Johannes Berg" <johannes.berg@...el.com>, "Linus Torvalds"
> > > <torvalds@...ux-foundation.org>, "Peter Zijlstra"
> > > <peterz@...radead.org>, "Thomas Gleixner" <tglx@...utronix.de>, "Greg
> > > Kroah-Hartman" <gregkh@...uxfoundation.org>,
> > > "lttng-dev" <lttng-dev@...ts.lttng.org>, "Rusty Russell"
> > > <rusty@...tcorp.com.au>, "Andi Kleen" <andi@...stfloor.org>
> > > Sent: Wednesday, March 12, 2014 4:35:15 PM
> > > Subject: Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not
> > > set via debugfs
> > > 
> > > > So I understand that you wish to banish tracepoints from static inline
> > > > functions within headers to ensure they only appear within a single
> > > > module.
> > > > This seems to be a step backward, but let's assume we stick to that
> > > > rule.
> > > > Then how do you envision dealing with Link-Time Optimisations (LTO) ?
> > > 
> > > I assume it uses the file name defines set by Kbuild?
> > 
> > Just to make sure I understand your question: I understand that you are
> > asking
> > whether tracepoints use file name defines at all in the naming of a
> > tracepoint.
> > The answer to this question is: No, they do not.
> 
> Ok. It uses kallsyms? That can change of course.

As I just replied to Steven, I now see that I mixed up concerns about
static keys, and the prior kernel markers, with tracepoint concerns.
The way they are implemented are very much different (Hey! I should know,
I wrote that code some 6 years ago!) ;)

> > 
> > > These don't change with
> > > LTO. It's whatever was specified at compile time. Also LTO doesn't
> > > inline over module boundaries (if the module is not built in)
> > 
> > Good to know. Can it inline core kernel functions into a module ?
> 
> Each module and the main kernel are currently LTO'ed separately.
> 
> In theory it would be possible to change this, but likely at some
> compile time cost.

OK, thanks for the explanations!

Mathieu

> 
> -Andi
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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