Re: inotify to minimize stat() calls

On Sun, Feb 10, 2013 at 11:58 PM, Erik Faye-Lund [off-list ref] wrote:

Karsten Blees has done something similar-ish on Windows, and he posted
the results here:

https://groups.google.com/forum/#!topic/msysgit/fL_jykUmUNE/discussion

I also seem to remember he doing a ReadDirectoryChangesW version, but
I don't remember what happened with that.

Thanks. I came across that but did not remember. For one thing, we
know the inotify alternative for Windows: ReadDirectoryChangesW.

But the meat of the patch is not about that function. In fact it's
dropped in fscache-v3 [1]. It seems that doing
FindFirstFile/FindNextFile for an entire directory, cache the results
and use it to simulate lstat() is faster on Windows. Sounds similar to
preload-index. And because directory listing is cached anyway,
opendir/readdir is replaced to read from cache instead of opening the
directory again.

So it is orthogonal with using ReadDirectoryChangesW/inotify to
further reduce the system calls.

I copy "git status"'s (impressive) numbers from fscache-v0 for those
who are interested in:

preload | -u  | normal | cached | gain
--------+-----+--------+--------+------
false   | all | 25.144 | 3.055  |  8.2
false   | no  | 22.822 | 1.748  | 12.8
true    | all |  9.234 | 2.179  |  4.2
true    | no  |  6.833 | 0.955  |  7.2

[1] https://github.com/kblees/git/commit/35f319609aa046d2350db32d3afa1fa44920e880
-- 
Duy