X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fust-metadata.c;h=f430ae1f1e8ed390df410b71370f1771286afc66;hb=8f0044bfed9f5ca51eab51478f483f92cc8f84a7;hp=2735169747e9bfc8108cb5e009cd8a922eefffa8;hpb=7972aab22f74b18faa168c0482216a3dd711a075;p=lttng-tools.git

diff --git a/src/bin/lttng-sessiond/ust-metadata.c b/src/bin/lttng-sessiond/ust-metadata.c
index 273516974..f430ae1f1 100644
--- a/src/bin/lttng-sessiond/ust-metadata.c
+++ b/src/bin/lttng-sessiond/ust-metadata.c
@@ -37,6 +37,13 @@
 #define max_t(type, a, b)	((type) ((a) > (b) ? (a) : (b)))
 #endif
 
+#define NR_CLOCK_OFFSET_SAMPLES		10
+
+struct offset_sample {
+	uint64_t offset;		/* correlation offset */
+	uint64_t measure_delta;		/* lower is better */
+};
+
 static inline
 int fls(unsigned int x)
 {
@@ -490,37 +497,65 @@ int _lttng_event_header_declare(struct ust_registry_session *session)
 	);
 }
 
-/*
- * Approximation of NTP time of day to clock monotonic correlation,
- * taken at start of trace.
- * Yes, this is only an approximation. Yes, we can (and will) do better
- * in future versions.
- */
 static
-uint64_t measure_clock_offset(void)
+int measure_single_clock_offset(struct offset_sample *sample)
 {
-	uint64_t offset, monotonic[2], realtime;
+	uint64_t offset, monotonic[2], measure_delta, realtime;
 	struct timespec rts = { 0, 0 };
 	int ret;
 
 	monotonic[0] = trace_clock_read64();
 	ret = clock_gettime(CLOCK_REALTIME, &rts);
-	if (ret < 0)
-		return 0;
+	if (ret < 0) {
+		return ret;
+	}
 	monotonic[1] = trace_clock_read64();
+	measure_delta = monotonic[1] - monotonic[0];
+	if (measure_delta > sample->measure_delta) {
+		/*
+		 * Discard value if it took longer to read than the best
+		 * sample so far.
+		 */
+		return 0;
+	}
 	offset = (monotonic[0] + monotonic[1]) >> 1;
 	realtime = (uint64_t) rts.tv_sec * 1000000000ULL;
 	realtime += rts.tv_nsec;
 	offset = realtime - offset;
-	return offset;
+	sample->offset = offset;
+	sample->measure_delta = measure_delta;
+	return 0;
 }
 
+/*
+ * Approximation of NTP time of day to clock monotonic correlation,
+ * taken at start of trace. Keep the measurement that took the less time
+ * to complete, thus removing imprecision caused by preemption.
+ */
+static
+uint64_t measure_clock_offset(void)
+{
+	int i;
+	struct offset_sample offset_best_sample = {
+		.offset = 0,
+		.measure_delta = UINT64_MAX,
+	};
+
+	for (i = 0; i < NR_CLOCK_OFFSET_SAMPLES; i++) {
+		if (measure_single_clock_offset(&offset_best_sample)) {
+			return 0;
+		}
+	}
+	return offset_best_sample.offset;
+}
 
 /*
  * Should be called with session registry mutex held.
  */
 int ust_metadata_session_statedump(struct ust_registry_session *session,
-		struct ust_app *app)
+		struct ust_app *app,
+		uint32_t major,
+		uint32_t minor)
 {
 	unsigned char *uuid_c;
 	char uuid_s[UUID_STR_LEN],
@@ -529,7 +564,6 @@ int ust_metadata_session_statedump(struct ust_registry_session *session,
 	char hostname[HOST_NAME_MAX];
 
 	assert(session);
-	assert(app);
 
 	uuid_c = session->uuid;
 
@@ -585,12 +619,10 @@ int ust_metadata_session_statedump(struct ust_registry_session *session,
 		"	domain = \"ust\";\n"
 		"	tracer_name = \"lttng-ust\";\n"
 		"	tracer_major = %u;\n"
-		"	tracer_minor = %u;\n"
-		"	tracer_patchlevel = %u;\n",
+		"	tracer_minor = %u;\n",
 		hostname,
-		app->version.major,
-		app->version.minor,
-		app->version.patchlevel
+		major,
+		minor
 		);
 	if (ret)
 		goto end;
@@ -601,8 +633,10 @@ int ust_metadata_session_statedump(struct ust_registry_session *session,
 	 */
 	if (app) {
 		ret = lttng_metadata_printf(session,
+			"	tracer_patchlevel = %u;\n"
 			"	vpid = %d;\n"
 			"	procname = \"%s\";\n",
+			app->version.patchlevel,
 			(int) app->pid,
 			app->name
 			);