linux-kernel - Re: [PATCH] x86: add the debugfs interface for the sysprof tool

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Date:	Tue, 26 Feb 2008 09:55:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Nicholas Miell <nmiell@...cast.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, sandmann@...hat.com, tglx@...x.de,
	hpa@...or.com, levon@...ementarian.org
Subject: Re: [PATCH] x86: add the debugfs interface for the sysprof tool


* Pekka Enberg <penberg@...helsinki.fi> wrote:

> Hi,
> 
> On Tue, Feb 26, 2008 at 8:27 AM, Pekka Enberg <penberg@...helsinki.fi> wrote:
> > >  You could try passing the --callgraph option to opcontrol.
> >
> >  Hmm, perhaps I am missing something but I don't think that does what
> >  sysprof does. At least I can't find where in the oprofile kernel code
> >  does it save the full stack trace for user-space. John?
> 
> Ok, so as pointed out by Nicholas/Andrew, oprofile does indeed do 
> exactly what sysprof does (see 
> arch/x86/oprofile/backtrace.c::backtrace_address, for example). So, 
> Soeren, any other reason we can't use the oprofile kernel module for 
> sysprof?

as i pointed it out earlier in the thread, the oprofile implementation 
seems buggy because when an event comes from NMI context 
__copy_from_user_inatomic() can fault and re-enable NMIs - causing 
possible stack recursion/corruption. Does not look like an easy fix.

	Ingo
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