From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936818AbdJQQVc (ORCPT ); Tue, 17 Oct 2017 12:21:32 -0400 Received: from mail-wr0-f195.google.com ([209.85.128.195]:49788 "EHLO mail-wr0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965357AbdJQQV2 (ORCPT ); Tue, 17 Oct 2017 12:21:28 -0400 X-Google-Smtp-Source: ABhQp+TZnHcAAzaFOQ0+7RdW0Ei9PFCfe5WNW0KjMzfwTiVUl31OOGe9fo4TYxtA5d90bCN5+kK0Qg== Date: Tue, 17 Oct 2017 18:21:24 +0200 From: Ingo Molnar To: Thomas Gleixner Cc: Byungchul Park , johan@kernel.org, arnd@arndb.de, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, peterz@infradead.org, hpa@zytor.com, tony@atomide.com, linux-tip-commits@vger.kernel.org, kernel-team@lge.com Subject: Re: [tip:locking/urgent] locking/lockdep: Disable cross-release features for now Message-ID: <20171017162124.n6epaodlx3q56xw4@gmail.com> References: <20171014072659.f2yr6mhm5ha3eou7@gmail.com> <20171016020447.GP3323@X58A-UD3R> <20171017071202.6x22ho2o5yz74dak@gmail.com> <20171017144230.dwrrxnpseo7tv6rp@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Thomas Gleixner wrote: > On Tue, 17 Oct 2017, Ingo Molnar wrote: > > * Thomas Gleixner wrote: > > > On Tue, 17 Oct 2017, Ingo Molnar wrote: > > > > No, please fix performance. > > > > > > You know very well that with the cross release stuff we have to take the > > > performance hit of stack unwinding because we have no idea whether there > > > will show up a new lock relation later or not. And there is not much you > > > can do in that respect. > > > > > > OTOH, the cross release feature unearthed real deadlocks already so it is a > > > valuable debug feature and having an explicit config switch which defaults > > > to N is well worth it. > > > > I disagree, because even if that's correct, the choices are not binary. The > > performance regression was a slowdown of around 7x: lockdep boot overhead on that > > particula system went from +3 seconds to +21 seconds... > > Hmm, I might have missed something, but what I've seen in this thread is: > > > > > Boot time (from "Linux version" to login prompt) had in fact doubled > > > > since 4.13 where it took 17 seconds (with my current config) compared to > > > > the 35 seconds I now see with 4.14-rc4. > > So that's 2x not 7x. [...] Yeah, so what you missed I think is that the no-lockdep bootup time is 14 seconds. So we have: vanilla: 14 secs lockdep: 17 secs (+3 secs) lockdep+crossrelease: 35 secs (+21 secs) So lockdep overhead got 7x worse on this system. Thanks, Ingo