On Mon, Feb 11, 2013 at 3:16 AM, Junio C Hamano <gits...@pobox.com> wrote:
> The other "lstat()" experiment was a very interesting one, but this
> is not yet an interesting experiment to see where in the "ignore"
> codepath we are spending times.
> We know that we can tell wt_status_collect_untracked() not to bother
> with the untracked or ignored files with !s->show_untracked_files
> already, but I think the more interesting question is if we can show
> the untracked files with less overhead.
> If we want to show untrackedd files, it is a given that we need to
> read directories to see what paths there are on the filesystem. Is
> the opendir/readdir cost dominating in the process? Are we spending
> a lot of time sifting the result of opendir/readdir via the ignore
> mechanism? Is reading the "ignore" files costing us much to prime
> the ignore mechanism?
> If readdir cost is dominant, then that makes "cache gitignore" a
> nonsense proposition, I think.  If you really want to "cache"
> something, you need to have somebody (i.e. a daemon) who constantly
> keeps an eye on the filesystem changes and can respond with the up
> to date result directly to fill_directory().  I somehow doubt that
> it is a direction we would want to go in, though.

Yeah, it did not cut out syscall cost, I also cut a lot of user-space
processing (plus .gitignore content access). From the timings I posted

>         unmodified  dir.c
> real    0m0.550s    0m0.287s
> user    0m0.305s    0m0.201s
> sys     0m0.240s    0m0.084s

sys time is reduced from 0.24s to 0.08s, so readdir+opendir definitely
has something to do with it (and perhaps reading .gitignore). But it
also reduces user time from 0.305 to 0.201s. I don't think avoiding
readdir+openddir will bring us this gain. It's probably the cost of
matching .gitignore. I'll try to replace opendir+readdir with a
no-syscall version. At this point "untracked caching" sounds more
feasible (and less complex) than ".gitignore cachine".
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