read-cache: log the number of lstat calls to trace2

Report the total number of calls made to lstat() inside of refresh_index().

FSMonitor improves the performance of commands like `git status` by
avoiding scanning the disk for changed files.  This can be seen in
`refresh_index()`.  Let's measure this.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/read-cache.c b/read-cache.c
index ecf6f689940556977974a48fe44b2b20f31b9bf5..893cc41e1d93eedae4ef7b4c9a84ac1a971d0a6f 100644 (file)
--- a/read-cache.c
+++ b/read-cache.c
@@ -1364,7 +1364,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 static struct cache_entry *refresh_cache_ent(struct index_state *istate,
                                             struct cache_entry *ce,
                                             unsigned int options, int *err,
-                                            int *changed_ret)
+                                            int *changed_ret,
+                                            int *t2_did_lstat)
 {
        struct stat st;
        struct cache_entry *updated;
@@ -1406,6 +1407,8 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
                return NULL;
        }
 
+       if (t2_did_lstat)
+               *t2_did_lstat = 1;
        if (lstat(ce->name, &st) < 0) {
                if (ignore_missing && errno == ENOENT)
                        return ce;
@@ -1519,6 +1522,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
        const char *added_fmt;
        const char *unmerged_fmt;
        struct progress *progress = NULL;
+       int t2_sum_lstat = 0;
 
        if (flags & REFRESH_PROGRESS && isatty(2))
                progress = start_delayed_progress(_("Refresh index"),
@@ -1536,11 +1540,13 @@ int refresh_index(struct index_state *istate, unsigned int flags,
         * we only have to do the special cases that are left.
         */
        preload_index(istate, pathspec, 0);
+       trace2_region_enter("index", "refresh", NULL);
        for (i = 0; i < istate->cache_nr; i++) {
                struct cache_entry *ce, *new_entry;
                int cache_errno = 0;
                int changed = 0;
                int filtered = 0;
+               int t2_did_lstat = 0;
 
                ce = istate->cache[i];
                if (ignore_submodules && S_ISGITLINK(ce->ce_mode))
@@ -1566,7 +1572,10 @@ int refresh_index(struct index_state *istate, unsigned int flags,
                if (filtered)
                        continue;
 
-               new_entry = refresh_cache_ent(istate, ce, options, &cache_errno, &changed);
+               new_entry = refresh_cache_ent(istate, ce, options,
+                                             &cache_errno, &changed,
+                                             &t2_did_lstat);
+               t2_sum_lstat += t2_did_lstat;
                if (new_entry == ce)
                        continue;
                if (progress)
@@ -1602,6 +1611,8 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 
                replace_index_entry(istate, i, new_entry);
        }
+       trace2_data_intmax("index", NULL, "refresh/sum_lstat", t2_sum_lstat);
+       trace2_region_leave("index", "refresh", NULL);
        if (progress) {
                display_progress(progress, istate->cache_nr);
                stop_progress(&progress);
@@ -1614,7 +1625,7 @@ struct cache_entry *refresh_cache_entry(struct index_state *istate,
                                        struct cache_entry *ce,
                                        unsigned int options)
 {
-       return refresh_cache_ent(istate, ce, options, NULL, NULL);
+       return refresh_cache_ent(istate, ce, options, NULL, NULL, NULL);
 }