While some of these issues have been discussed in other threads, I
thought I'd summarize my thoughts here.
On 1/26/2018 7:28 PM, Ævar Arnfjörð Bjarmason wrote:
I just got around to testing this since it landed, for context some
previous poking of mine in [1].
Issues / stuff I've noticed:
1) We end up invalidating the untracked cache because stuff in .git/
changed. For example:
01:09:24.975524 fsmonitor.c:173 fsmonitor process '.git/hooks/fsmonitor-watchman' returned success
01:09:24.975548 fsmonitor.c:138 fsmonitor_refresh_callback '.git'
01:09:24.975556 fsmonitor.c:138 fsmonitor_refresh_callback '.git/config'
01:09:24.975568 fsmonitor.c:138 fsmonitor_refresh_callback '.git/index'
01:09:25.122726 fsmonitor.c:91 write fsmonitor extension successful
Am I missing something or should we do something like:
diff --git a/fsmonitor.c b/fsmonitor.c
index 0af7c4edba..5067b89bda 100644
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -118,7 +118,12 @@ static int query_fsmonitor(int version, uint64_t last_update, struct strbuf *que
static void fsmonitor_refresh_callback(struct index_state *istate, const char *name)
{
- int pos = index_name_pos(istate, name, strlen(name));
+ int pos;
+
+ if (!strcmp(name, ".git") || starts_with(name, ".git/"))
+ return;
+
+ pos = index_name_pos(istate, name, strlen(name));
if (pos >= 0) {
struct cache_entry *ce = istate->cache[pos];
With that patch applied status on a large repo[2] goes from a consistent
~180-200ms to ~140-150ms, since we're not invalidating some of the UC
structure
I favor making this optimization by updating
untracked_cache_invalidate_path() so that it ignores paths under
get_git_dir() and doesn't invalidate the untracked cache or flag the
index as dirty.
2) We re-write out the index even though we know nothing changed
When you first run with core.fsmonitor it needs to
mark_fsmonitor_clean() for every path, but is there a reason for why we
wouldn't supply the equivalent of GIT_OPTIONAL_LOCKS=0 if all paths are
marked and we know from the hook that nothing changed? Why write out the
index again?
Writing out the index when core.fsmonitor is first turned on is
necessary to get the index extension added with the current state of the
dirty flags. Given it is a one time cost, I don't think we have
anything worth trying to optimize here.
3) A lot of time spend reading the index (or something..)
While the hook itself takes ~20ms (and watchman itself 1/4 of that)
status as a whole takes much longer. gprof reveals:
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
15.38 0.02 0.02 221690 0.00 0.00 memihash
15.38 0.04 0.02 221689 0.00 0.00 create_from_disk
7.69 0.05 0.01 2216897 0.00 0.00 git_bswap32
7.69 0.06 0.01 222661 0.00 0.00 ce_path_match
7.69 0.07 0.01 221769 0.00 0.00 hashmap_add
7.69 0.08 0.01 39941 0.00 0.00 prep_exclude
7.69 0.09 0.01 39940 0.00 0.00 strbuf_addch
7.69 0.10 0.01 1 10.00 10.00 read_one
7.69 0.11 0.01 1 10.00 10.00 refresh_index
7.69 0.12 0.01 1 10.00 10.00 tweak_fsmonitor
7.69 0.13 0.01 preload_thread
The index is 24M in this case, I guess it's unpacking it, but I wonder
if this couldn't be much faster if we saved away the result of the last
"status" in something that's quick to access, and then if nothing
changed we just report that, and no need to re-write the index (or just
write the "it was clean at this time" part).
Yes, reading the index is slow. We've made some improvements (not
computing the SHA, not validating the sort order, etc) and have one more
in progress that will reduce the malloc() cost. I haven't found any
other easy optimizations but it would be great if you could find more!
To make significant improvements, I'm afraid it will take more
substantial changes to the in memory and on disk formats and updates to
the code to take advantage of those changes.
4) core.fsmonitor=false behaves unexpectedly
The code that reads this variable just treats it as a string, so we do a
bunch of work for nothing (and nothing warns) if this is set and 'false'
is executed. Any reason we couldn't do our standard boolean parsing
here? You couldn't call your hook 0/1/true/false, but that doesn't seem
like a big loss.
1. https://public-inbox.org/git/CACBZZX5a6Op7dH_g9WOFBnejh2zgNK4b34ygxA8daNDqvitFVA@xxxxxxxxxxxxxx/
2. https://github.com/avar/2015-04-03-1M-git
I'm torn on this one. The core.fsmontior setting isn't a boolean value,
its a string that is the command to run when we need file system
changes. It would be pretty simple to add a call to
git_parse_maybe_bool_text() to treat "false," "no," or "off" the same as
an empty string but that makes it look even more like a boolean when it
isn't.
