From 344dc5d3c7b5a64eef0252b9b73e9925bbb6a5f7 Mon Sep 17 00:00:00 2001
From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date: Thu, 4 Sep 2008 07:30:19 +0200
Subject: [PATCH] --- yaml --- r: 111533 b: refs/heads/master c:
 f76fd327a8b32d3ad5b51639faf6f54d18be0981 h: refs/heads/master i:   111531:
 eabb3145a04439f7484392d63b95480c4a50d482 v: v3

---
 [refs]                       |  2 +-
 trunk/net/dccp/ccids/ccid3.c | 13 +++++++++++++
 trunk/net/dccp/dccp.h        |  5 ++++-
 trunk/net/dccp/timer.c       |  3 +--
 4 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/[refs] b/[refs]
index c7e79cc7c2e4..b93909f7856a 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 7d1af6a8d935678248d057564e75e1452409a53c
+refs/heads/master: f76fd327a8b32d3ad5b51639faf6f54d18be0981
diff --git a/trunk/net/dccp/ccids/ccid3.c b/trunk/net/dccp/ccids/ccid3.c
index 0d406f82e433..f566eb76aeb2 100644
--- a/trunk/net/dccp/ccids/ccid3.c
+++ b/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);
diff --git a/trunk/net/dccp/dccp.h b/trunk/net/dccp/dccp.h
index 1585fa26488c..b63a82ccb2b2 100644
--- a/trunk/net/dccp/dccp.h
+++ b/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)
 
diff --git a/trunk/net/dccp/timer.c b/trunk/net/dccp/timer.c
index e02d5a94f4c0..16359e29e7f5 100644
--- a/trunk/net/dccp/timer.c
+++ b/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);