From 05e002cd4241ea2a39771364f1b1c16b33c170f8 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Thu, 16 Dec 2010 18:27:38 +0100
Subject: [PATCH] Delay selecting source on start

On start, when servers are reachable and use the same polling interval,
wait for them to have the same reachability register (which corresponds
to the number of samples in sourcestats) before selecting one.
---
 sources.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/sources.c b/sources.c
index af90aec..170710e 100644
--- a/sources.c
+++ b/sources.c
@@ -423,6 +423,8 @@ SRC_SelectSource(unsigned long match_addr)
   int min_distance_index;
   struct SelectInfo *si;
   double total_root_dispersion;
+  int n_badstats_sources;
+  int max_sel_reach, max_badstat_reach;
 
   NTP_Leap leap_status = LEAP_Normal;
   old_selected_index = selected_source_index;
@@ -442,6 +444,8 @@ SRC_SelectSource(unsigned long match_addr)
   /* Step 1 - build intervals about each source */
   n_endpoints = 0;
   n_sel_sources = 0;
+  n_badstats_sources = 0;
+  max_sel_reach = max_badstat_reach = 0;
   for (i=0; i<n_sources; i++) {
 
     if (sources[i]->selectable && sources[i]->reachability &&
@@ -487,8 +491,16 @@ SRC_SelectSource(unsigned long match_addr)
 
         n_endpoints += 2;
 
+        if (max_sel_reach < sources[i]->reachability) {
+          max_sel_reach = sources[i]->reachability;
+        }
       } else {
+        ++n_badstats_sources;
         sources[i]->status = SRC_BAD_STATS;
+
+        if (max_badstat_reach < sources[i]->reachability) {
+          max_badstat_reach = sources[i]->reachability;
+        }
       }
     } else {
       /* If the source is not reachable, there is no way we will pick
@@ -497,6 +509,23 @@ SRC_SelectSource(unsigned long match_addr)
     }
   }
 
+#if 0
+  LOG(LOGS_INFO, LOGF_Sources, "badstat_sources=%d sel_sources=%d badstat_reach=%x sel_reach=%x",
+      n_badstats_sources, n_sel_sources, max_badstat_reach, max_sel_reach);
+#endif
+
+  /* Wait for the next call if we have no source selected and there is
+     a source with bad stats (has less than 3 samples) with reachability
+     equal to shifted maximum reachability of sources with valid stats.
+     This delays selecting source on start with servers using the same
+     polling interval until they all have valid stats. */
+
+  if (n_badstats_sources && n_sel_sources &&
+      selected_source_index == INVALID_SOURCE && 
+      max_sel_reach >> 1 == max_badstat_reach) {
+    return;
+  }
+
 #if 0
   LOG(LOGS_INFO, LOGF_Sources, "n_endpoints=%d", n_endpoints);
 #endif