netdev - Re: netlink stats and message ordering.

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Date:	Sat, 20 Nov 2010 05:49:02 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	NetDev <netdev@...r.kernel.org>
Subject: Re: netlink stats and message ordering.

Le vendredi 19 novembre 2010 à 10:20 -0800, Ben Greear a écrit :
> I have a single netlink socket that listens for various things,
> as well as requests netdev stats and such.
> 
> I am seeing a case during interface creation (mac-vlans) where I get one set of stats
> that appears to show 1 packet transmitted, and then immediately after that,
> a second set of stats for the same device that shows all zero counters.
> 
> Since I'm trying to handle wraps properly, my code tends to consider this
> a wrap and of course the numbers go all wrong since it wasn't really a wrap.
> 
> I am wondering if it's possible that netlink messages are somehow being
> re-ordered before they are sent to my application?

That's strange, maybe you could add a timestamp (or a sequence number)
in the stats message to check if two messages are eventually re-ordered.

As a fast check you could try to increment an error counter like this.
If you see the rx_dropped going back, then for sure there is a
problem...

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 93f0ba2..1d271ca 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -444,6 +444,7 @@ static struct rtnl_link_stats64 *macvlan_dev_get_stats64(struct net_device *dev,
 {
 	struct macvlan_dev *vlan = netdev_priv(dev);
 
+	atomic_long_inc(&dev->rx_dropped);
 	if (vlan->pcpu_stats) {
 		struct macvlan_pcpu_stats *p;
 		u64 rx_packets, rx_bytes, rx_multicast, tx_packets, tx_bytes;


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