Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753463Ab1EGG6W (ORCPT ); Sat, 7 May 2011 02:58:22 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:48365 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752812Ab1EGG6V (ORCPT ); Sat, 7 May 2011 02:58:21 -0400 Date: Sat, 7 May 2011 08:58:03 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Steven Rostedt , Arjan van de Ven , linux-kernel , Frederic Weisbecker , Peter Zijlstra , Thomas Gleixner Subject: Re: Fix powerTOP regression with 2.6.39-rc5 Message-ID: <20110507065803.GA23414@elte.hu> References: <4DC45537.6070609@linux.intel.com> <1304713252.25414.2532.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2457 Lines: 58 * Linus Torvalds wrote: > On Fri, May 6, 2011 at 1:20 PM, Steven Rostedt wrote: > > > > I strongly NACK this! > > Doesn't matter. > > Binary compatibility is more important. Yes, absolutely, violently agreed. Acked-by: Ingo Molnar Steve, we had this argument again and again internally, and you still do not seem to understand it: viable tooling is *way* more important than the short-term, marginal cleanliness interests of kernel developers. We wont be able to merge ftrace into perf until you understand this principle ... Arjan, Steve, i think we need to create a 'perf test' testcase for ftrace events as well, to catch such ABI breakages faster, hm? It took a couple of months for this breakage to surface and that's clearly too slow. > And if binaries don't use the interface to parse the format (or just parse it > wrongly - see the fairly recent example of adding uuid's to > /proc/self/mountinfo), then it's a regression. > > And regressions get reverted, unless there are security issues or similar > that makes us go "Oh Gods, we really have to break things". > > I don't understand why this simple logic is so hard for some kernel > developers to understand. Reality matters. Your personal wishes matter NOT AT > ALL. You have just summed up the main philosophical difference between perf and ftrace: with perf we have a "sane tooling first" approach, while ftrace is still the old "kernel developers first" approach. In the past 10 years i pushed tons of instrumentation code upstream and for a long time the kernel-integrated ftrace approach looked like the technical best solution to me, but after 2 years of sane instrumentation tooling via a proper user-space ABI and tools/perf/ i'm not looking back. I am strongly convinced that we need to bite the bullet and unify the two approaches to enable even better tooling: expose the remaining bits of tracing functionality not available via perf yet via the perf ABI and move it under a single umbrella, slowly phase out the ABI-unstable /debug/tracing/ debugfs crap for new features and use the strict perf ABI approach. Steve? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/