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.
