netlink stats and message ordering.
Subsystems (2)
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?
Thanks,
Ben
Signature · 2 lines
Ben Greear <[email protected]> Candela Technologies Inc http://www.candelatech.com
Quoted 7 lines · Ben Greear
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.
Quoted 5 lines
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...
drivers/net/macvlan.c +1 -0
@@ -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;
Quoted 8 lines · Eric Dumazet
Quoted 7 lines · Ben Greear
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.
Quoted 8 lines
Quoted 5 lines
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.
I am becoming suspicious that I may have a re-entrancy issue in my code..maybe while handling a dev-create message I am calling into the netlink-read logic again before handling all of the messages that were read in the initial call.
I'm going to have to think on this more, and if nothing obvious comes up, I'll try your suggestion for incrementing one of the stats by one each time.
Thanks,
Ben
Quoted 14 lines
drivers/net/macvlan.c +1
-0@@ -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;
Signature · 2 lines
Ben Greear <[email protected]> Candela Technologies Inc http://www.candelatech.com