[SCTP] Add jitter to the heartbeat interval. (ardelle.fan)

Per RFC 2960 (well, impl-guide corrections really) add a jitter in the
range of -50% to +50% of the current rto to the heartbeat interval. 

include/net/sctp/sctp.h

@@ -2,7 +2,7 @@
  * Copyright (c) 1999-2000 Cisco, Inc.
  * Copyright (c) 1999-2001 Motorola, Inc.
  * Copyright (c) 2001-2003 International Business Machines, Corp.
- * Copyright (c) 2001 Intel Corp.
+ * Copyright (c) 2001-2003 Intel Corp.
  *
  * This file is part of the SCTP kernel reference Implementation
  *
@@ -38,6 +38,7 @@
  *    Jon Grimm             <jgrimm@us.ibm.com>
  *    Daisy Chang           <daisyc@us.ibm.com>
  *    Sridhar Samudrala     <sri@us.ibm.com>
+ *    Ardelle Fan           <ardelle.fan@intel.com>
  *
  * Any bugs reported given to us we will try to fix... any fixes shared will
  * be incorporated into the next SCTP release.
@@ -422,6 +423,23 @@ static inline size_t get_user_iov_size(struct iovec *iov, int iovlen)
 	return retval;
 }
 
+/* Generate a random jitter in the range of -50% ~ +50% of input RTO. */
+static inline __s32 sctp_jitter(__u32 rto)
+{
+	static __u32 sctp_rand;
+	__s32 ret;
+
+	sctp_rand += jiffies;
+	sctp_rand ^= (sctp_rand << 12);
+	sctp_rand ^= (sctp_rand >> 20);
+
+	/* Choose random number from 0 to rto, then move to -50% ~ +50% 
+	 * of rto. 
+	 */
+	ret = sctp_rand % rto - (rto >> 1);
+	return ret;
+}
+
 /* Walk through a list of TLV parameters.  Don't trust the
  * individual parameter lengths and instead depend on
  * the chunk length to indicate when to stop.  Make sure

net/sctp/sm_sideeffect.c

@@ -1134,8 +1134,8 @@ static void sctp_cmd_hb_timers_start(sctp_cmd_seq_t *cmds,
 	 */
 	list_for_each(pos, &asoc->peer.transport_addr_list) {
 		t = list_entry(pos, sctp_transport_t, transports);
-		if (!mod_timer(&t->hb_timer,
-			       t->hb_interval + t->rto + jiffies)) {
+		if (!mod_timer(&t->hb_timer, t->hb_interval + t->rto + 
+				sctp_jitter(t->rto) + jiffies)) {
 			sctp_transport_hold(t);
 		}
 	}
@@ -1147,7 +1147,8 @@ static void sctp_cmd_hb_timers_update(sctp_cmd_seq_t *cmds,
 				   sctp_transport_t *t)
 {
 	/* Update the heartbeat timer.  */
-	if (!mod_timer(&t->hb_timer, t->hb_interval + t->rto + jiffies))
+	if (!mod_timer(&t->hb_timer, t->hb_interval + t->rto + 
+			sctp_jitter(t->rto) + jiffies))
 		sctp_transport_hold(t);
 }
 

net/sctp/transport.c

@@ -42,6 +42,7 @@
  *    Xingang Guo           <xingang.guo@intel.com>
  *    Hui Huang             <hui.huang@nokia.com>
  *    Sridhar Samudrala	    <sri@us.ibm.com>
+ *    Ardelle Fan	    <ardelle.fan@intel.com>
  *
  * Any bugs reported given to us we will try to fix... any fixes shared will
  * be incorporated into the next SCTP release.
@@ -184,8 +185,9 @@ void sctp_transport_reset_timers(sctp_transport_t *transport)
 	}
 
 	/* When a data chunk is sent, reset the heartbeat interval.  */
-	if (!mod_timer(&transport->hb_timer,
-		       transport->hb_interval + transport->rto + jiffies))
+	if (!mod_timer(&transport->hb_timer, transport->hb_interval +
+			transport->rto  + sctp_jitter(transport->rto) +
+			jiffies))
 		sctp_transport_hold(transport);
 }