From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965842AbcA1Oi3 (ORCPT ); Thu, 28 Jan 2016 09:38:29 -0500 Received: from mail.efficios.com ([78.47.125.74]:60099 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965670AbcA1OiX (ORCPT ); Thu, 28 Jan 2016 09:38:23 -0500 Date: Thu, 28 Jan 2016 14:38:16 +0000 (UTC) From: Mathieu Desnoyers To: Peter Zijlstra Cc: rostedt , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, "Paul E. McKenney" Message-ID: <1616014588.6697.1453991896740.JavaMail.zimbra@efficios.com> In-Reply-To: <20160128135733.GQ6356@twins.programming.kicks-ass.net> References: <20160128080859.GB6357@twins.programming.kicks-ass.net> <1069612139.6639.1453988280286.JavaMail.zimbra@efficios.com> <20160128135733.GQ6356@twins.programming.kicks-ass.net> Subject: Re: [RFC][BUG] tracer: Fails to work MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [78.47.125.74] X-Mailer: Zimbra 8.6.0_GA_1178 (ZimbraWebClient - FF44 (Linux)/8.6.0_GA_1178) Thread-Topic: tracer: Fails to work Thread-Index: gplp3xb1iT9lU2OtccFijtnFxM1a3Q== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jan 28, 2016, at 8:57 AM, Peter Zijlstra peterz@infradead.org wrote: > On Thu, Jan 28, 2016 at 01:38:00PM +0000, Mathieu Desnoyers wrote: > >> Thoughts ? > > So ideally dumping the trace data would not depend on any of that, > because I can break it all :-) > > Not being able to access the trace data completely and utterly defeats > the purpose of having a tracer in the first place. One item I have on my todo list is to allow mapping the tracer buffers (lttng in my case) onto RAM that persists across reboots/kexec using dax and the pmem driver. Since the original system is clearly inactive after a reboot, we can read the buffers from memory without caring about synchronization. That would be one possible way of handling your snapshot-of-buggy-kernel-trace-buffers use-case. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com