On Wed, Jun 30 2021, Junio C Hamano wrote:

* jh/builtin-fsmonitor (2021-05-24) 30 commits
 - t/perf: avoid copying builtin fsmonitor files into test repo
 - t7527: test status with untracked-cache and fsmonitor--daemon
 - p7519: add fsmonitor--daemon
 - t7527: create test for fsmonitor--daemon
 - fsmonitor: force update index after large responses
 - fsmonitor: enhance existing comments
 - fsmonitor--daemon: use a cookie file to sync with file system
 - fsmonitor--daemon: periodically truncate list of modified files
 - fsmonitor--daemon: implement handle_client callback
 - fsmonitor-fs-listen-macos: implement FSEvent listener on MacOS
 - fsmonitor-fs-listen-macos: add macos header files for FSEvent
 - fsmonitor-fs-listen-win32: implement FSMonitor backend on Windows
 - fsmonitor--daemon: create token-based changed path cache
 - fsmonitor--daemon: define token-ids
 - fsmonitor--daemon: add pathname classification
 - fsmonitor--daemon: implement daemon command options
 - fsmonitor-fs-listen-macos: stub in backend for MacOS
 - fsmonitor-fs-listen-win32: stub in backend for Windows
 - t/helper/fsmonitor-client: create IPC client to talk to FSMonitor Daemon
 - fsmonitor--daemon: implement client command options
 - fsmonitor--daemon: add a built-in fsmonitor daemon
 - fsmonitor: introduce `core.useBuiltinFSMonitor` to call the daemon via IPC
 - config: FSMonitor is repository-specific
 - help: include fsmonitor--daemon feature flag in version info
 - fsmonitor-ipc: create client routines for git-fsmonitor--daemon
 - fsmonitor--daemon: update fsmonitor documentation
 - fsmonitor--daemon: man page
 - simple-ipc: preparations for supporting binary messages.
 - Merge branch 'jk/perf-in-worktrees' into HEAD
 - Merge branch 'jh/simple-ipc' into jh/rfc-builtin-fsmonitor

 An attempt to write and ship with a watchman equivalent tailored
 for our use.

 What's the status of this one?

I think Johannes's reply to the last WC applies[1]:

    I am not Jeff, but I know that he is busy getting back to it, and
    plans on submitting a third iteration.

FWIW I'm still curious about some details on the performance concerns
that seem to have prompted this built-in fsmonitor endeavor, as I asked
about (but didn't get a reply to) in [2].

Not as a "we shouldn't have this, let's keep using the hook", but just
curiosity about why we've seemingly gotten such different performance
numbers on the watchman hook v.s. a built-in approach.

I suspect (but don't know) that the reason is that the built-in is
perhaps integrating differently with git somehow, in a way that we could
retrofit the hook approach to also do (if anyone still cares about the
hook approach).

In any case I'm interested in *why* the new approach is faster, given
that I've done some testing (again, noted in [2]) that suggest that
bottleneck in the previous pipeline wasn't at all what Jeff H. thought
it was.

1. https://lore.kernel.org/git/nycvar.QRO.7.76.6.2106171135530.57@tvgsbejvaqbjf.bet/#t (local)
2. https://lore.kernel.org/git/87h7lgfchm.fsf@evledraar.gmail.com/ (local)