From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935862AbZFOV7n (ORCPT ); Mon, 15 Jun 2009 17:59:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754110AbZFOV7h (ORCPT ); Mon, 15 Jun 2009 17:59:37 -0400 Received: from tomts5.bellnexxia.net ([209.226.175.25]:42180 "EHLO tomts5-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755979AbZFOV7g (ORCPT ); Mon, 15 Jun 2009 17:59:36 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AokFAMdgNkpMQWQl/2dsb2JhbACBT9MXhA0F Date: Mon, 15 Jun 2009 17:54:20 -0400 From: Mathieu Desnoyers To: "H. Peter Anvin" Cc: Ingo Molnar , Peter Zijlstra , Linus Torvalds , mingo@redhat.com, paulus@samba.org, acme@redhat.com, linux-kernel@vger.kernel.org, penberg@cs.helsinki.fi, vegard.nossum@gmail.com, efault@gmx.de, jeremy@goop.org, npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods Message-ID: <20090615215420.GE12919@Krystal> References: <20090615185907.GF6520@Krystal> <1245092561.6741.205.camel@laptop> <4A369CD8.3090505@zytor.com> <20090615192720.GA9056@Krystal> <4A36A1C7.6080005@zytor.com> <20090615210119.GD24554@elte.hu> <20090615211207.GB12919@Krystal> <20090615211605.GC27100@elte.hu> <20090615213429.GD12919@Krystal> <4A36BF61.10901@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <4A36BF61.10901@zytor.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 17:50:04 up 107 days, 18:16, 3 users, load average: 0.36, 0.28, 0.27 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * H. Peter Anvin (hpa@zytor.com) wrote: > Mathieu Desnoyers wrote: > > > > As the maintainer of the out-of-tree LTTng tracer, which hooks in the > > page fault handler with tracepoints, and which can build almost entirely > > as modules, I am very tempted to argue that having the nmi-code entirely > > robust wrt in-kernel page faults would be a very-nice-to-have feature. > > > > I doubt that is ever going to be reliable, due to reentrancy issues. > > -hpa Do you mean the page fault handler code is no ever going to be reliable or the tracer code ? I spent a great deal of effort making LTTng lockless and reentrant wrt NMIs. It would be great if the low-level kernel exception handlers would do the same, therefore I would not have to isolate the tracer from the kernel as I currently do. Well, I would still continue to isolate the tracer from the kernel, but at least I would not have to spend as much effort controlling what exceptions and faults paths the tracer is executing. Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68