---

yaml
---
r: 111533
b: refs/heads/master
c: f76fd32
h: refs/heads/master
i:
  111531: eabb314
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 7d1af6a8d935678248d057564e75e1452409a53c
+refs/heads/master: f76fd327a8b32d3ad5b51639faf6f54d18be0981

trunk/net/dccp/ccids/ccid3.c

@@ -869,6 +869,19 @@ MODULE_PARM_DESC(ccid3_debug, "Enable debug messages");
 
 static __init int ccid3_module_init(void)
 {
+	struct timespec tp;
+
+	/*
+	 * Without a fine-grained clock resolution, RTTs/X_recv are not sampled
+	 * correctly and feedback is sent either too early or too late.
+	 */
+	hrtimer_get_res(CLOCK_MONOTONIC, &tp);
+	if (tp.tv_sec || tp.tv_nsec > DCCP_TIME_RESOLUTION * NSEC_PER_USEC) {
+		printk(KERN_ERR "%s: Timer too coarse (%ld usec), need %u-usec"
+		       " resolution - check your clocksource.\n", __func__,
+		       tp.tv_nsec/NSEC_PER_USEC, DCCP_TIME_RESOLUTION);
+		return -ESOCKTNOSUPPORT;
+	}
 	return ccid_register(&ccid3);
 }
 module_init(ccid3_module_init);

trunk/net/dccp/dccp.h

@@ -86,10 +86,13 @@ extern void dccp_time_wait(struct sock *sk, int state, int timeo);
  */
 #define DCCP_RTO_MAX ((unsigned)(64 * HZ))
 
+/* DCCP base time resolution - 10 microseconds (RFC 4340, 13.1 ... 13.3) */
+#define DCCP_TIME_RESOLUTION	10
+
 /*
  * RTT sampling: sanity bounds and fallback RTT value from RFC 4340, section 3.4
  */
-#define DCCP_SANE_RTT_MIN	100
+#define DCCP_SANE_RTT_MIN	(10 * DCCP_TIME_RESOLUTION)
 #define DCCP_FALLBACK_RTT	(USEC_PER_SEC / 5)
 #define DCCP_SANE_RTT_MAX	(3 * USEC_PER_SEC)
 

trunk/net/dccp/timer.c

@@ -281,8 +281,7 @@ u32 dccp_timestamp(void)
 {
 	s64 delta = ktime_us_delta(ktime_get_real(), dccp_timestamp_seed);
 
-	do_div(delta, 10);
-	return delta;
+	return div_u64(delta, DCCP_TIME_RESOLUTION);
 }
 EXPORT_SYMBOL_GPL(dccp_timestamp);