[LARTC] tc counters "problem"

[Francisco]

Hi, I'm using tc and HTB to shape my outgoing ADSL traffic. I was trying to 
make some graphs on the classes by meassuring the "sent bytes" of each class 
using rrdtool to store the data (as kbps after conversion). I expected that 
meassuring the root class I would get values similar that the ones I get 
measuring the interface counters but they differ by a large amount.
Is there something obvious I'm missing here?, is this approach correct?
Thank you.

Francisco

kaori ~ # tc -s class show dev ppp0
class htb 1:1 root rate 200000bit ceil 200000bit burst 6Kb/8 mpu 0b overhead 
0b cburst 1699b/8 mpu 0b overhead 0b level 7
 Sent 378286130 bytes 2185057 pkt (dropped 0, overlimits 0 requeues 0)
 rate 182312bit 29pps backlog 0b 0p requeues 0
 lended: 0 borrowed: 0 giants: 0
 tokens: 168756 ctokens: -13270

class htb 1:10 parent 1:1 leaf 10: prio 1 rate 200000bit ceil 200000bit burst 
6Kb/8 mpu 0b overhead 0b cburst 1699b/8 mpu 0b overhead 0b level 0
 Sent 115548283 bytes 1520567 pkt (dropped 0, overlimits 0 requeues 0)
 rate 1848bit 4pps backlog 0b 0p requeues 0
 lended: 1520567 borrowed: 0 giants: 0
 tokens: 250020 ctokens: 67994

class htb 1:20 parent 1:1 leaf 20: prio 2 rate 180000bit ceil 180000bit burst 
6Kb/8 mpu 0b overhead 0b cburst 1689b/8 mpu 0b overhead 0b level 0
 Sent 262755089 bytes 664505 pkt (dropped 0, overlimits 0 requeues 0)
 rate 180456bit 25pps backlog 0b 15p requeues 0
 lended: 664490 borrowed: 0 giants: 0
 tokens: 113243 ctokens: -89463

class htb 1:30 parent 1:1 leaf 30: prio 3 rate 1000bit ceil 120000bit burst 
6Kb/8 mpu 0b overhead 0b cburst 1659b/8 mpu 0b overhead 0b level 0
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0
 lended: 0 borrowed: 0 giants: 0
 tokens: 50331648 ctokens: 113321

class htb 1:40 parent 1:1 leaf 40: prio 4 rate 1000bit ceil 60000bit burst 
6Kb/8 mpu 0b overhead 0b cburst 1629b/8 mpu 0b overhead 0b level 0
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0
 lended: 0 borrowed: 0 giants: 0
 tokens: 50331648 ctokens: 222548