Add small randomness to spacing between samples for one server

broadcast.c

@@ -121,7 +121,7 @@ timeout_handler(void *arbitrary)
 
   /* Requeue timeout.  Don't care if interval drifts gradually, so just do it
    * at the end. */
-  SCH_AddTimeoutInClass((double) d->interval, 1.0,
+  SCH_AddTimeoutInClass((double) d->interval, 1.0, 0.02,
                         SCH_NtpBroadcastClass,
                         timeout_handler, (void *) d);
 
@@ -148,7 +148,7 @@ BRD_AddDestination(IPAddr *addr, unsigned short port, int interval)
   destinations[n_destinations].addr.port = port;
   destinations[n_destinations].interval = interval;
 
-  SCH_AddTimeoutInClass((double) interval, 1.0,
+  SCH_AddTimeoutInClass((double) interval, 1.0, 0.0,
                         SCH_NtpBroadcastClass,
                         timeout_handler, (void *)(destinations + n_destinations));
   

ntp_core.c

@@ -178,6 +178,9 @@ struct NCR_Instance_Record {
    minimise risk of network collisions) (in seconds) */
 #define SAMPLING_SEPARATION 0.2
 
+/* Randomness added to spacing between samples for one server/peer */
+#define SAMPLING_RANDOMNESS 0.02
+
 /* Spacing between samples in burst mode for one server/peer */
 #define BURST_INTERVAL 2.0
 
@@ -247,6 +250,7 @@ start_initial_timeout(NCR_Instance inst)
 
   /* Start timer for first transmission */
   inst->timeout_id = SCH_AddTimeoutInClass(INITIAL_DELAY, SAMPLING_SEPARATION,
+                                           SAMPLING_RANDOMNESS,
                                            SCH_NtpSamplingClass,
                                            transmit_timeout, (void *)inst);
   inst->timer_running = 1;
@@ -622,6 +626,7 @@ transmit_timeout(void *arg)
     /* Requeue timeout */
     inst->timer_running = 1;
     inst->timeout_id = SCH_AddTimeoutInClass(WARM_UP_DELAY, SAMPLING_SEPARATION,
+                                             SAMPLING_RANDOMNESS,
                                              SCH_NtpSamplingClass,
                                              transmit_timeout, (void *)inst);
 
@@ -707,6 +712,7 @@ transmit_timeout(void *arg)
   if (do_timer) {
     inst->timer_running = 1;
     inst->timeout_id = SCH_AddTimeoutInClass(timeout_delay, SAMPLING_SEPARATION,
+                                             SAMPLING_RANDOMNESS,
                                              SCH_NtpSamplingClass,
                                              transmit_timeout, (void *)inst);
   } else {
@@ -1259,6 +1265,7 @@ receive_packet(NTP_Packet *message, struct timeval *now, double now_err, NCR_Ins
     /* Get rid of old timeout and start a new one */
     SCH_RemoveTimeout(inst->timeout_id);
     inst->timeout_id = SCH_AddTimeoutInClass(delay_time, SAMPLING_SEPARATION,
+                                             SAMPLING_RANDOMNESS,
                                              SCH_NtpSamplingClass,
                                              transmit_timeout, (void *)inst);
   }
@@ -1818,6 +1825,7 @@ NCR_InitiateSampleBurst(NCR_Instance inst, int n_good_samples, int n_total_sampl
         }
         inst->timer_running = 1;
         inst->timeout_id = SCH_AddTimeoutInClass(0.0, SAMPLING_SEPARATION,
+                                                 SAMPLING_RANDOMNESS,
                                                  SCH_NtpSamplingClass,
                                                  transmit_timeout, (void *) inst);
         break;
@@ -1831,6 +1839,7 @@ NCR_InitiateSampleBurst(NCR_Instance inst, int n_good_samples, int n_total_sampl
         }
         inst->timer_running = 1;
         inst->timeout_id = SCH_AddTimeoutInClass(0.0, SAMPLING_SEPARATION,
+                                                 SAMPLING_RANDOMNESS,
                                                  SCH_NtpSamplingClass,
                                                  transmit_timeout, (void *) inst);
         break;

sched.c

@@ -129,6 +129,7 @@ handle_slew(struct timeval *raw,
 void
 SCH_Initialise(void)
 {
+  struct timeval tv;
 
   FD_ZERO(&read_fds);
   n_read_fds = 0;
@@ -143,6 +144,9 @@ SCH_Initialise(void)
 
   LCL_AddParameterChangeHandler(handle_slew, NULL);
 
+  LCL_ReadRawTime(&tv);
+  srandom(tv.tv_sec * tv.tv_usec);
+
   initialised = 1;
 
   return;
@@ -322,18 +326,24 @@ SCH_AddTimeoutByDelay(double delay, SCH_TimeoutHandler handler, SCH_ArbitraryArg
 /* ================================================== */
 
 SCH_TimeoutID
-SCH_AddTimeoutInClass(double min_delay, double separation,
+SCH_AddTimeoutInClass(double min_delay, double separation, double randomness,
                       SCH_TimeoutClass class,
                       SCH_TimeoutHandler handler, SCH_ArbitraryArgument arg)
 {
   TimerQueueEntry *new_tqe;
   TimerQueueEntry *ptr;
   struct timeval now;
-  double diff;
+  double diff, r;
   double new_min_delay;
 
   assert(initialised);
 
+  if (randomness > 0.0) {
+    r = random() % 0xffff / (0xffff - 1.0) * randomness + 1.0;
+    min_delay *= r;
+    separation *= r;
+  }
+  
   LCL_ReadRawTime(&now);
   new_min_delay = min_delay;
 

sched.h

@@ -72,8 +72,9 @@ extern SCH_TimeoutID SCH_AddTimeoutByDelay(double delay, SCH_TimeoutHandler, SCH
 
 /* This queues a timeout in a particular class, ensuring that the
    expiry time is at least a given separation away from any other
-   timeout in the same class */
+   timeout in the same class, given randomness is added to the delay
-extern SCH_TimeoutID SCH_AddTimeoutInClass(double min_delay, double separation,
+   and separation */
+extern SCH_TimeoutID SCH_AddTimeoutInClass(double min_delay, double separation, double randomness,
                                            SCH_TimeoutClass class,
                                            SCH_TimeoutHandler handler, SCH_ArbitraryArgument);