linux-kernel - Re: [PATCHv9 2.6.35-rc4-tip 10/13] perf: Re-Add make_absolute

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Date:	Wed, 14 Jul 2010 16:50:02 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Naren A Devaiah <naren.devaiah@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCHv9 2.6.35-rc4-tip 10/13]  perf: Re-Add make_absolute_path

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Arnaldo Carvalho de Melo <acme@...radead.org> wrote:
> 
> > Em Tue, Jul 13, 2010 at 10:49:27PM -0400, Steven Rostedt escreveu:
> > > On Mon, 2010-07-12 at 13:12 -0300, Arnaldo Carvalho de Melo wrote:
> > > > Em Mon, Jul 12, 2010 at 10:30:36AM -0400, Steven Rostedt escreveu:
> > 
> > > > Well, I prefer to follow the kernel way of doing things, i.e. to
> > > > propagate as much as possible up the callchain the error return value,
> > > > so that the apps can handle it in any way they prefer, i.e. die() calls
> > > > in tools/perf/builtin-foo.c are okayish, but not on tools/perf/util/.
> > 
> > > Ah, yes, die is a bit strong. And I have been starting to avoid them
> > > too. Although, when malloc fails, it's almost certain that the app will
> > > die soon anyway ;-)
> > 
> > The interesting thing is that years ago, when modules were being introduced 
> > in the kernel and panic() calls for things like out of memory conditions 
> > were being removed, some people made the same comments, 'if that happens, 
> > you're doomed anyway!' :-)
> > 
> > I can see things like trying to load a huge perf.data file in the TUI 
> > interface failing and the user just being warned about it and going on with 
> > life loading some other file, etc.
> > 
> > Certainly it is interesting to try to apply as much as possible of the 
> > mindset (and fear of criticism) present when coding for the kernel when one 
> > codes for userland.
> 
> Yeah, and especially for perf the absolutely most important quality is 
> reliability. It's not just an app - it's a measurement tool. People rely on it 
> to reject or apply patches, on a daily basis.
> 
> perf must be very reliable and very dependable (and i'm happy that we managed 
> to achieve that goal so far :), and if it fails it should be apparent that it 
> failed and that results should not be relied on.
> 
> With other tools that are statistical i've sometimes seen a special type of 
> dangerous attitude of: "hey, it's just a sample, no biggie if it's lost, it's 
> just statistical anyway, lost in the noise" - but that's really a slippery 
> slope leading to a sloppy tool we cannot depend on 110%.
> 
> Just like physicists or engineers want to be able to trust their measurement 
> instruments, do we want kernel hackers to be able to trust the results of 
> perf.

I'm glad to see we're on the exact same page here. :)

Having reliable trace analysis tools is crucially important for both kernel
developers and end-users, especially when, as an example, someone try to use the
results to find out which is the "one" odd-case longest/shortest interrupt
handler during a day-long trace while trying to pinpoint a bug.

Thanks,

Mathieu

> 
> Thanks,
> 
> 	Ingo

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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