From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C0AFC004D4 for ; Thu, 19 Jan 2023 09:05:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229851AbjASJFt (ORCPT ); Thu, 19 Jan 2023 04:05:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60672 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229986AbjASJFh (ORCPT ); Thu, 19 Jan 2023 04:05:37 -0500 Received: from lgeamrelo11.lge.com (lgeamrelo13.lge.com [156.147.23.53]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6BBFD68404 for ; Thu, 19 Jan 2023 01:05:25 -0800 (PST) Received: from unknown (HELO lgemrelse6q.lge.com) (156.147.1.121) by 156.147.23.53 with ESMTP; 19 Jan 2023 18:05:24 +0900 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO localhost.localdomain) (10.177.244.38) by 156.147.1.121 with ESMTP; 19 Jan 2023 18:05:24 +0900 X-Original-SENDERIP: 10.177.244.38 X-Original-MAILFROM: byungchul.park@lge.com From: Byungchul Park To: tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, damien.lemoal@opensource.wdc.com, linux-ide@vger.kernel.org, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, will@kernel.org, rostedt@goodmis.org, joel@joelfernandes.org, sashal@kernel.org, daniel.vetter@ffwll.ch, duyuyang@gmail.com, johannes.berg@intel.com, tj@kernel.org, tytso@mit.edu, willy@infradead.org, david@fromorbit.com, amir73il@gmail.com, gregkh@linuxfoundation.org, kernel-team@lge.com, linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@kernel.org, minchan@kernel.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com, sj@kernel.org, jglisse@redhat.com, dennis@kernel.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, vbabka@suse.cz, ngupta@vflare.org, linux-block@vger.kernel.org, paolo.valente@linaro.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, jlayton@kernel.org, dan.j.williams@intel.com, hch@infradead.org, djwong@kernel.org, dri-devel@lists.freedesktop.org, rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com, hamohammed.sa@gmail.com, 42.hyeyoo@gmail.com, chris.p.wilson@intel.com, gwan-gyeong.mun@intel.com, max.byungchul.park@gmail.com, boqun.feng@gmail.com, longman@redhat.com Subject: Re: [PATCH RFC v7 00/23] DEPT(Dependency Tracker) Date: Thu, 19 Jan 2023 18:05:11 +0900 Message-Id: <1674119111-12759-1-git-send-email-byungchul.park@lge.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <873588j92x.ffs@tglx> References: <873588j92x.ffs@tglx> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Thomas wrote: > On Tue, Jan 17 2023 at 10:18, Boqun Feng wrote: > > On Mon, Jan 16, 2023 at 10:00:52AM -0800, Linus Torvalds wrote: > > > I also recall this giving a fair amount of false positives, are they all fixed? > > > > From the following part in the cover letter, I guess the answer is no? > > ... > > 6. Multiple reports are allowed. > > 7. Deduplication control on multiple reports. > > 8. Withstand false positives thanks to 6. > > ... > > > > seems to me that the logic is since DEPT allows multiple reports so that > > false positives are fitlerable by users? > > I really do not know what's so valuable about multiple reports. They > produce a flood of information which needs to be filtered, while a > single report ensures that the first detected issue is dumped, which > increases the probability that it can be recorded and acted upon. Assuming the following 2 assumptions, you are right. Assumption 1. There will be too many reports with the multi-report support, like all the combination of dependencies between e.g. in-irq and irq-enabled-context. Assumption 2. The detection is matured enough so that it barely happens to fix false onces to see true one which is not a big deal. However, DEPT doesn't generate all the combination of irq things as Lockdep does so we only see a few multi-reports even with the support, and I admit DEPT hasn't matured enough yet because fine classification is required anyway to suppress false alarms. That's why I introduced multi-report support at least for now. IMHO, it'd be still useful even if it's gonna report a few true ones at once w/o false ones some day. > Filtering out false positives is just the wrong approach. Decoding > dependency issues from any tracker is complex enough given the nature of > the problem, so adding the burden of filtering out issues from a stream > of dumps is not helpful at all. It's just a marketing gag. > > > * Instead of introducing a brand new detector/dependency tracker, > > could we first improve the lockdep's dependency tracker? I think > > Byungchul also agrees that DEPT and lockdep should share the > > same dependency tracker and the benefit of improving the > > existing one is that we can always use the self test to catch > > any regression. Thoughts? > > Ack. If the internal implementation of lockdep has shortcomings, then we > can expand and/or replace it instead of having yet another > infrastructure which is not even remotely as mature. Ultimately, yes. We should expand or replace it instead of having another ultimately. Byungchul > > Thanks, > > tglx