Different git variants record file times in the index with different
precisions, according to their capabilities. E.g. git compiled with NO_NSEC
records seconds only, JGit records the mtime in milliseconds, but leaves
ctime blank (because ctime is unavailable in Java).
This causes performance issues in git compiled with USE_NSEC, because index
entries with such 'incomplete' timestamps are considered dirty, triggering
unnecessary content checks.
Add a file time comparison function that auto-detects the precision based
on the number of trailing 0 digits, and compares with the lower precision
of both values. This initial version supports the known precisions seconds
(git + NO_NSEC), milliseconds (JGit) and nanoseconds (git + USE_NSEC), but
can be easily extended to e.g. microseconds.
Use the new comparison function in both dirty and racy checks. As a side
effect, this fixes racy detection in USE_NSEC-enabled git with
core.checkStat=minimal, as the coreStat setting now affects racy checks as
well.
Finally, do not check ctime if ctime.sec is 0 (as recorded by JGit).
Signed-off-by: Karsten Blees <blees@xxxxxxx>
---
read-cache.c | 62 ++++++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 41 insertions(+), 21 deletions(-)
This patch fixes problems 3 and 4, by trying to auto-detect the recorded file
time precision.
diff --git a/read-cache.c b/read-cache.c
index 87204a5..3a4e6cd 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -99,23 +99,50 @@ void fill_stat_data(struct stat_data *sd, struct stat *st)
sd->sd_size = st->st_size;
}
+/*
+ * Compares two file times. Returns 0 if equal, <0 if t1 < t2, >0 if t1 > t2.
+ * Auto-detects precision based on trailing 0 digits. Compares seconds only if
+ * core.checkStat=minimal.
+ */
+static inline int cmp_filetime(uint32_t t1_sec, uint32_t t1_nsec,
+ uint32_t t2_sec, uint32_t t2_nsec) {
+#ifdef USE_NSEC
+ /*
+ * Compare seconds and return result if different, or checkStat=mimimal,
+ * or one of the time stamps has second precision only (nsec == 0).
+ */
+ int diff = t1_sec - t2_sec;
+ if (diff || !check_stat || !t1_nsec || !t2_nsec)
+ return diff;
+
+ /*
+ * Check if one of the time stamps has millisecond precision only (i.e.
+ * the trailing 6 digits are 0). First check the trailing 6 bits so that
+ * we only do (slower) modulo division if necessary.
+ */
+ if ((!(t1_nsec & 0x3f) && !(t1_nsec % 1000000)) ||
+ (!(t2_nsec & 0x3f) && !(t2_nsec % 1000000)))
+ /* Compare milliseconds. */
+ return (t1_nsec - t2_nsec) / 1000000;
+
+ /* Compare nanoseconds */
+ return t1_nsec - t2_nsec;
+#else
+ return t1_sec - t2_sec;
+#endif
+}
+
int match_stat_data(const struct stat_data *sd, struct stat *st)
{
int changed = 0;
- if (sd->sd_mtime.sec != (unsigned int)st->st_mtime)
- changed |= MTIME_CHANGED;
- if (trust_ctime && check_stat &&
- sd->sd_ctime.sec != (unsigned int)st->st_ctime)
- changed |= CTIME_CHANGED;
-
-#ifdef USE_NSEC
- if (check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
+ if (cmp_filetime(sd->sd_mtime.sec, sd->sd_mtime.nsec,
+ (unsigned) st->st_mtime, ST_MTIME_NSEC(*st)))
changed |= MTIME_CHANGED;
- if (trust_ctime && check_stat &&
- sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
+ if (trust_ctime && check_stat && sd->sd_ctime.sec &&
+ cmp_filetime(sd->sd_ctime.sec, sd->sd_ctime.nsec,
+ (unsigned) st->st_ctime, ST_CTIME_NSEC(*st)))
changed |= CTIME_CHANGED;
-#endif
if (check_stat) {
if (sd->sd_uid != (unsigned int) st->st_uid ||
@@ -276,16 +303,9 @@ static int ce_match_stat_basic(const struct cache_entry *ce, struct stat *st)
static int is_racy_stat(const struct index_state *istate,
const struct stat_data *sd)
{
- return (istate->timestamp.sec &&
-#ifdef USE_NSEC
- /* nanosecond timestamped files can also be racy! */
- (istate->timestamp.sec < sd->sd_mtime.sec ||
- (istate->timestamp.sec == sd->sd_mtime.sec &&
- istate->timestamp.nsec <= sd->sd_mtime.nsec))
-#else
- istate->timestamp.sec <= sd->sd_mtime.sec
-#endif
- );
+ return istate->timestamp.sec &&
+ (cmp_filetime(istate->timestamp.sec, istate->timestamp.nsec,
+ sd->sd_mtime.sec, sd->sd_mtime.nsec) <= 0);
}
static int is_racy_timestamp(const struct index_state *istate,
--
2.1.0.msysgit.0
--
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