From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934728AbZFOWZO (ORCPT ); Mon, 15 Jun 2009 18:25:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755729AbZFOWZC (ORCPT ); Mon, 15 Jun 2009 18:25:02 -0400 Received: from terminus.zytor.com ([198.137.202.10]:44356 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752022AbZFOWZA (ORCPT ); Mon, 15 Jun 2009 18:25:00 -0400 Message-ID: <4A36C953.8060906@zytor.com> Date: Mon, 15 Jun 2009 15:21:07 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Mathieu Desnoyers 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 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> <20090615215420.GE12919@Krystal> In-Reply-To: <20090615215420.GE12919@Krystal> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mathieu Desnoyers wrote: > * 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. > So instead you want to core kernel to do your work for you? -hpa