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Open Source and information security mailing list archives
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Date: Mon, 9 May 2022 18:28:17 -0400 From: "Theodore Ts'o" <tytso@....edu> To: Byungchul Park <byungchul.park@....com> Cc: torvalds@...ux-foundation.org, damien.lemoal@...nsource.wdc.com, linux-ide@...r.kernel.org, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, mingo@...hat.com, linux-kernel@...r.kernel.org, peterz@...radead.org, will@...nel.org, tglx@...utronix.de, rostedt@...dmis.org, joel@...lfernandes.org, sashal@...nel.org, daniel.vetter@...ll.ch, chris@...is-wilson.co.uk, duyuyang@...il.com, johannes.berg@...el.com, tj@...nel.org, willy@...radead.org, david@...morbit.com, amir73il@...il.com, bfields@...ldses.org, gregkh@...uxfoundation.org, kernel-team@....com, linux-mm@...ck.org, akpm@...ux-foundation.org, mhocko@...nel.org, minchan@...nel.org, hannes@...xchg.org, vdavydov.dev@...il.com, sj@...nel.org, jglisse@...hat.com, dennis@...nel.org, cl@...ux.com, penberg@...nel.org, rientjes@...gle.com, vbabka@...e.cz, ngupta@...are.org, linux-block@...r.kernel.org, paolo.valente@...aro.org, josef@...icpanda.com, linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk, jack@...e.cz, jack@...e.com, jlayton@...nel.org, dan.j.williams@...el.com, hch@...radead.org, djwong@...nel.org, dri-devel@...ts.freedesktop.org, airlied@...ux.ie, rodrigosiqueiramelo@...il.com, melissa.srw@...il.com, hamohammed.sa@...il.com, 42.hyeyoo@...il.com Subject: Re: [PATCH RFC v6 00/21] DEPT(Dependency Tracker) Oh, one other problem with DEPT --- it's SLOW --- the overhead is enormous. Using kvm-xfstests[1] running "kvm-xfstests smoke", here are some sample times: LOCKDEP DEPT Time to first test 49 seconds 602 seconds ext4/001 2 s 22 s ext4/003 2 s 8 s ext4/005 0 s 7 s ext4/020 1 s 8 s ext4/021 11 s 17 s ext4/023 0 s 83 s generic/001 4 s 76 s generic/002 0 s 11 s generic/003 10 s 19 s There are some large variations; in some cases, some xfstests take 10x as much time or more to run. In fact, when I first started the kvm-xfstests run with DEPT, I thought something had hung and that tests would never start. (In fact, with gce-xfstests the default watchdog "something has gone terribly wrong with the kexec" had fired, and I didn't get any test results using gce-xfstests at all. If DEPT goes in without any optimizations, I'm going to have to adjust the watchdogs timers for gce-xfstests.) The bottom line is that at the moment, between the false positives, and the significant overhead imposed by DEPT, I would suggest that if DEPT ever does go in, that it should be possible to disable DEPT and only use the existing CONFIG_PROVE_LOCKING version of LOCKDEP, just because DEPT is S - L - O - W. [1] https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md - Ted P.S. Darrick and I both have disabled using LOCKDEP by default because it slows down ext4 -g auto testing by a factor 2, and xfs -g auto testing by a factor of 3. So the fact that DEPT is a factor of 2x to 10x or more slower than LOCKDEP when running various xfstests tests should be a real concern.
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