From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934785Ab0KQPRE (ORCPT ); Wed, 17 Nov 2010 10:17:04 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:34400 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934755Ab0KQPRC (ORCPT ); Wed, 17 Nov 2010 10:17:02 -0500 X-Authority-Analysis: v=1.1 cv=6ptpMFIBtxRk0xdOb6IhJTbTLVRlKjWFes7R4SsWCrA= c=1 sm=0 a=VINkOuZDQI4A:10 a=Q9fys5e9bTEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=meVymXHHAAAA:8 a=3h2OZVCpzC4U1w4x6DYA:9 a=KYynBsFCo3jxtKjpDUcA:7 a=PPmsoscCd3HbLgSX-Muqt4KpIJEA:4 a=PUjeQqilurYA:10 a=jeBq3FmKZ4MA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Subject: Re: [RFC][PATCH 1/5] [PATCH 1/5] events: Add EVENT_FS the event filesystem From: Steven Rostedt To: Ingo Molnar Cc: Greg KH , linux-kernel@vger.kernel.org, Andrew Morton , Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Theodore Tso , Arjan van de Ven , Mathieu Desnoyers , Lin Ming , Arnaldo Carvalho de Melo , Peter Zijlstra , Christoph Hellwig In-Reply-To: <20101117150332.GA7603@elte.hu> References: <20101117005357.024472450@goodmis.org> <20101117005939.600541101@goodmis.org> <20101117033242.GB31335@suse.de> <20101117103914.GA21976@elte.hu> <1289996753.30543.35.camel@gandalf.stny.rr.com> <20101117150332.GA7603@elte.hu> Content-Type: text/plain; charset="ISO-8859-15" Date: Wed, 17 Nov 2010 10:16:59 -0500 Message-ID: <1290007019.30543.65.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-11-17 at 16:03 +0100, Ingo Molnar wrote: > * Steven Rostedt wrote: > > > Are these events now going to be labeled as stable? Is every tracepoint we have, > > much have the same data? Linus specifically said at Kernel Summit that he wants > > absolutely NO modules to have a stable tracepoint. > > I think you are worrying about the wrong things. > > I think Arjan's complaints at the KS stemmed from prior sporadic declarations on > lkml that there is no tracepoint ABI _at all_, and that powertop/latencytop could > break anytime. > > But in reality i strongly disagree with such declarations, and tracepoint data that > is used by PowerTop/timechart/latencytop or perf is and was an ABI, simple as that - > and i've been enforcing that for two years. (We have so few good instrumentation > tools that we _really_ dont want to break them.) > > At that point, realizing that we have an ABI for existing tools, i think it's > fundamentally misguided to go out on a limb trying to put barriers in the way of > other tools that do not even exist to begin with ... > > Our real problem with tracing is lack of relevance, lack of utility, lack of > punch-through analytical power. > > Trying to create a sandbox to _reduce utility_ is like the last step, and a really > optional step, when we have such variety that we want some control over it. It's > always expensive, it always reduces the tool space as collateral damage. > > So please dont think of sysfs or eventfs as a tool to restrict. Think of it as a > tool to _organize_. > > Again, i'd _LOVE_ to have the 'problem' of us having so many tools that analyze > application and kernel behavior in such a rich way that they use tracepoints that > were not supposed to be 'stable'. > > I simply dont see the 'problem' that is being solved here. We had a stable ABI and > we didnt break sysprof or powertop/latencytop in the past and wont break it in the > future either. What about a tool that picks up tracepoints that were only used by a developer for in-field debugging, and then that tracepoint disappears because of a design change. Is it OK for that tool to break with it? Do all tools that use tracepoints require a "check" feature? I guess the problem is that creators of the tools to analyze the kernel have no idea of what they can count on and what they can't. Do we need a process to have these tool creators request to developers to "keep this tracepoint"? -- Steve