X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=lib%2Fsflow_poller.c;h=092aad10a8f2fcea24859090f539068394e4033f;hb=01308c2bb5d7970c59ea3a61554ce58736dcc2a9;hp=ffd09d3c2ae777c634a7d98fb29493f5ab60922d;hpb=a4af00400a835eb87569ba40e21874c05e872c0f;p=sliver-openvswitch.git

diff --git a/lib/sflow_poller.c b/lib/sflow_poller.c
index ffd09d3c2..092aad10a 100644
--- a/lib/sflow_poller.c
+++ b/lib/sflow_poller.c
@@ -23,10 +23,10 @@ void sfl_poller_init(SFLPoller *poller,
 
     /* clear everything */
     memset(poller, 0, sizeof(*poller));
-  
+
     /* restore the linked list ptr */
     poller->nxt = nxtPtr;
-  
+
     /* now copy in the parameters */
     poller->agent = agent;
     poller->dsi = dsi; /* structure copy */
@@ -68,10 +68,29 @@ u_int32_t sfl_poller_get_sFlowCpInterval(SFLPoller *poller) {
 
 void sfl_poller_set_sFlowCpInterval(SFLPoller *poller, u_int32_t sFlowCpInterval) {
     poller->sFlowCpInterval = sFlowCpInterval;
-    /* Set the countersCountdown to be a randomly selected value between 1 and
-       sFlowCpInterval. That way the counter polling would be desynchronised
-       (on a 200-port switch, polling all the counters in one second could be harmful). */
-    poller->countersCountdown = 1 + (random() % sFlowCpInterval);
+    if(sFlowCpInterval) {
+        /* Set the countersCountdown to be a randomly selected value between 1 and
+	   sFlowCpInterval. That way the counter polling will be desynchronised
+	   (on a 200-port switch, polling all the counters in one second could be harmful).
+	   In a large network, even this might not be ideal if time-synchroniziation
+	   between devices is close and counters are always polled on second boundaries. If
+	   1000 different devices all send an sFlow datagram on the same second boundary
+	   it could result in an antisocial burst.
+	   However when counter-samples are packed into the export datagram they do not
+	   always result in that datagram being sent immediately. It is more likely that
+	   a subsequent packet-sample will be the one that triggers the datagram to be sent.
+	   The packet-sample events are not sychronized to any clock, so that results in
+	   excellent desynchronization (http://blog.sflow.com/2009/05/measurement-traffic.html).
+	   Another smoothing factor is that the tick() function called here is usually
+	   driven from a fairly "soft" polling loop rather than a hard real-time event.
+	*/
+        poller->countersCountdown = 1 + (random() % sFlowCpInterval);
+    }
+    else {
+        /* Setting sFlowCpInterval to 0 disables counter polling altogether.  Thanks to
+	   Andy Kitchingman for spotting this ommission. */
+        poller->countersCountdown = 0;
+    }
 }
 
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