timedated: ignore initial delta in history data

[elogind.git] / src / timedate / timedate-sntp.c

diff --git a/src/timedate/timedate-sntp.c b/src/timedate/timedate-sntp.c
index e47a0865673185143efb5f3fab4c8abfab7c29cc..a85b37775290146f5afefab2cd5caa00b4ed9ef8 100644 (file)
--- a/src/timedate/timedate-sntp.c
+++ b/src/timedate/timedate-sntp.c
@@ -59,24 +59,24 @@
 #define ADJ_SETOFFSET                   0x0100  /* add 'time' to current time */
 #endif
 
-/* Maximum delta in seconds which the system clock is gradually adjusted
- * to approach the network time. Deltas larger that this are set by letting
- * the system time jump. The maximum for adjtime is 500ms.
- */
-#define NTP_MAX_ADJUST                  0.2
+/* expected accuracy of time synchronization; used to adjust the poll interval */
+#define NTP_ACCURACY_SEC                0.2
 
 /*
- * "Define the required accuracy of the system clock, then calculate the
- * maximum timeout. Use the longest maximum timeout possible given the system
- * constraints to minimize time server aggregate load."
- *
  * "A client MUST NOT under any conditions use a poll interval less
  * than 15 seconds."
  */
-#define NTP_POLL_INTERVAL_MIN_SEC       16
+#define NTP_POLL_INTERVAL_MIN_SEC       32
 #define NTP_POLL_INTERVAL_MAX_SEC       2048
-#define NTP_ACCURACY_SEC                0.1
 
+/*
+ * Maximum delta in seconds which the system clock is gradually adjusted
+ * (slew) to approach the network time. Deltas larger that this are set by
+ * letting the system time jump. The kernel's limit for adjtime is 0.5s.
+ */
+#define NTP_MAX_ADJUST                  0.4
+
+/* NTP protocol, packet header */
 #define NTP_LEAP_PLUSSEC                1
 #define NTP_LEAP_MINUSSEC               2
 #define NTP_LEAP_NOTINSYNC              3
@@ -399,6 +399,12 @@ static bool sntp_sample_spike_detection(SNTPContext *sntp, double offset, double
         double jitter;
         double j;
 
+        sntp->packet_count++;
+
+        /* ignore initial sample */
+        if (sntp->packet_count == 1)
+                return false;
+
         /* store the current data in our samples array */
         idx_cur = sntp->samples_idx;
         idx_new = (idx_cur + 1) % ELEMENTSOF(sntp->samples);
@@ -406,10 +412,8 @@ static bool sntp_sample_spike_detection(SNTPContext *sntp, double offset, double
         sntp->samples[idx_new].offset = offset;
         sntp->samples[idx_new].delay = delay;
 
-        sntp->packet_count++;
-        jitter = sntp->samples_jitter;
-
         /* calculate new jitter value from the RMS differences relative to the lowest delay sample */
+        jitter = sntp->samples_jitter;
         for (idx_min = idx_cur, i = 0; i < ELEMENTSOF(sntp->samples); i++)
                 if (sntp->samples[i].delay > 0 && sntp->samples[i].delay < sntp->samples[idx_min].delay)
                         idx_min = i;
@@ -666,7 +670,7 @@ int sntp_server_connect(SNTPContext *sntp, const char *server) {
         sntp->server_addr.sin_family = AF_INET;
         sntp->server_addr.sin_addr.s_addr = inet_addr(server);
 
-        sntp->poll_interval_usec = 2 * NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
+        sntp->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
 
         return sntp_send_request(sntp);
 }