linux-kernel - Re: [tip:tracing/core] x86, bts: reenable ptrace branch trace support

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Message-ID: <20090610125108.GA13506@elte.hu>
Date:	Wed, 10 Jun 2009 14:51:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	markus.t.metzger@...el.com, tglx@...utronix.de, oleg@...hat.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:tracing/core] x86, bts: reenable ptrace branch trace
	support


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, 2009-05-07 at 09:25 +0000, tip-bot for Markus Metzger wrote:
> > Commit-ID:  7e0bfad24d85de7cf2202a7b0ce51de11a077b21
> > Gitweb:     http://git.kernel.org/tip/7e0bfad24d85de7cf2202a7b0ce51de11a077b21
> > Author:     Markus Metzger <markus.t.metzger@...el.com>
> > AuthorDate: Fri, 24 Apr 2009 09:44:48 +0200
> > Committer:  Ingo Molnar <mingo@...e.hu>
> > CommitDate: Fri, 24 Apr 2009 10:18:51 +0200
> > 
> > x86, bts: reenable ptrace branch trace support
> > 
> > The races found by Oleg Nesterov have been fixed.
> > 
> > Reenable branch trace support.
> > 
> > Signed-off-by: Markus Metzger <markus.t.metzger@...el.com>
> > Acked-by: Oleg Nesterov <oleg@...hat.com>
> > LKML-Reference: <20090424094448.A30216@...ona.ch.intel.com>
> > Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> OK, this whole BTS thing worries me because it seems to expose too 
> much of the Intel Debug Store thingy to the outside world.
> 
> The thing is, once we do PEBS from inside the kernel, we'll have 
> to share the debug store, and the way this thing sets it up isn't 
> really going to work.
> 
> So what I'd like to see is having this debug store removed from 
> the interface and abstracted away as cpu resource -- a single page 
> when in use should suffice I think.
> 
> If you want to expose a buffer to userspace, use the regular 
> mmap() interface and fill those pages from the DS interrupt 
> handler.

hm, that makes sense indeed. We are in the merge window now - 
Markus, what's your suggestion?

	Ingo
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