From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752120AbdJSILE (ORCPT ); Thu, 19 Oct 2017 04:11:04 -0400 Received: from mail-wm0-f42.google.com ([74.125.82.42]:49808 "EHLO mail-wm0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751779AbdJSIK5 (ORCPT ); Thu, 19 Oct 2017 04:10:57 -0400 X-Google-Smtp-Source: ABhQp+TW50nSX3VpgkpL4tV1w3nVFOENBh0JPhmHRNxNqdpb+wXRH3FnesuIExkaBb4njCXs+u9ArA== Date: Thu, 19 Oct 2017 10:10:53 +0200 From: Ingo Molnar To: Byungchul Park Cc: peterz@infradead.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@lge.com, Linus Torvalds Subject: Re: [PATCH 1/2] lockdep: Introduce CROSSRELEASE_STACK_TRACE and make it not unwind as default Message-ID: <20171019081053.2mmzzjgfwgtv5lz3@gmail.com> References: <1508318006-2090-1-git-send-email-byungchul.park@lge.com> <20171018100944.g2mc6yorhtm5piom@gmail.com> <20171019043240.GA3310@X58A-UD3R> <20171019055730.mlpoz333ekflacs2@gmail.com> <20171019061112.GB3310@X58A-UD3R> <20171019062255.GC3310@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171019062255.GC3310@X58A-UD3R> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Byungchul Park wrote: > On Thu, Oct 19, 2017 at 03:11:12PM +0900, Byungchul Park wrote: > > On Thu, Oct 19, 2017 at 07:57:30AM +0200, Ingo Molnar wrote: > > > > > > * Byungchul Park wrote: > > > > > > > On Wed, Oct 18, 2017 at 12:09:44PM +0200, Ingo Molnar wrote: > > > > > BTW., have you attempted limiting the depth of the stack traces? I suspect more > > > > > than 2-4 are rarely required to disambiguate the calling context. > > > > > > > > I did it for you. Let me show you the result. > > > > > > > > 1. No lockdep: 2.756558155 seconds time elapsed ( +- 0.09% ) > > > > 2. Lockdep: 2.968710420 seconds time elapsed ( +- 0.12% ) > > > > 3. Lockdep + Crossrelease 5 entries: 3.153839636 seconds time elapsed ( +- 0.31% ) > > > > 4. Lockdep + Crossrelease 3 entries: 3.137205534 seconds time elapsed ( +- 0.87% ) > > > > 5. Lockdep + Crossrelease + This patch: 2.963669551 seconds time elapsed ( +- 0.11% ) > > > > > > I think the lockdep + crossrelease + full-stack numbers are missing? > > > > Ah, the last version of crossrelease merged into vanilla, records 5 > > entries, since I thought it overloads too much if full stack is used, > > and 5 entries are enough. Don't you think so? > > > > > But yeah, looks like single-entry-stacktrace crossrelease only has a +0.2% > > > performance cost (with 0.1% noise), while lockdep itself has a +7.7% cost. > > > > > > That's very reasonable and we can keep the single-entry cross-release feature > > > enabled by default as part of CONFIG_PROVE_LOCKING=y - assuming all the crashes > > > > BTW, is there any crash by cross-release I don't know? Of course, I know > > cases of false positives, but I don't about crash. > > Are you talking about the oops by 'null pointer dereference' by unwinder a > few weeks ago? > > At the time, cross-release was falsely accused. AFAIK, cross-release has > not crashed system yet. I'm talking about the crash fixed here: 8b405d5c5d09: locking/lockdep: Fix stacktrace mess Which was introduced by your patch: ce07a9415f26: locking/lockdep: Make check_prev_add() able to handle external stack_trace ... which was a preparatory patch for cross-release. So 'technically' it's not a cross-release crash, but was very much related. It even says so in the changelog: Actually crossrelease needs to do other than saving a stack_trace. So pass a stack_trace and callback to handle it, to check_prev_add(). ... so let's not pretend it wasn't related, ok? Thanks, Ingo