[ovs-dev] [PATCH] datapath: Correctly report flow used times for first 5 minutes after boot.

[Ben Pfaff]

The kernel starts out its "jiffies" timer as 5 minutes below zero, as
shown in include/linux/jiffies.h:

  /*
   * Have the 32 bit jiffies value wrap 5 minutes after boot
   * so jiffies wrap bugs show up earlier.
   */
  #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))

The loop in ovs_flow_stats_get() starts out with 'used' set to 0, then
takes any "later" time.  This means that for the first five minutes after
boot, flows will always be reported as never used, since 0 is greater than
any time already seen.

Signed-off-by: Ben Pfaff <blp at nicira.com>
---
 datapath/flow.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/datapath/flow.c b/datapath/flow.c
index c3e3fcb..e9a2a27 100644
--- a/datapath/flow.c
+++ b/datapath/flow.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2007-2013 Nicira, Inc.
+ * Copyright (c) 2007-2014 Nicira, Inc.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of version 2 of the GNU General Public
@@ -148,7 +148,7 @@ void ovs_flow_stats_get(struct sw_flow *flow, struct ovs_flow_stats *ovs_stats,
 			 * block bottom-halves here.
 			 */
 			spin_lock_bh(&stats->lock);
-			if (time_after(stats->used, *used))
+			if (!*used || time_after(stats->used, *used))
 				*used = stats->used;
 			*tcp_flags |= stats->tcp_flags;
 			ovs_stats->n_packets += stats->packet_count;
-- 
1.7.10.4