I am using Traffic Control on a modem with a 2.6.26 kernel. When I intentionally send more data to the modem (4Mbit to class 9997:9999) using iperf than the capacity of the system (2700Kbit), I see that excess traffic is usually dropped by traffic control but occasionally traffic control stops sending any data of any class to the interface. Please see the qdisc and class statistics (sampled every second) below when the traffic is stopped. I have verified that traffic is coming into the modem during this period. I have also found that if I use a filter to drop the excess traffic to class 9997:9999 that this does not occur.

When it is in this state, I can see from the data below that while classes 9997:1, 9997:2, 9997:3, and 9997:9999 show no increase in data sent or dropped, their parent, 9997:9998, reports data being sent with nothing dropped. Does this make sense?

Why does traffic control stop sending all data? Shouldn't it continue to simply drop the excess data and continue to send data at least at the minimum rate?




qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 69550950 bytes 46010 pkt (dropped 44815, overlimits 95450 requeues 0)
rate 0bit 0pps backlog 0b 999p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 35364630 bytes 23400 pkt (dropped 44932, overlimits 0 requeues 0)
rate 1199Kbit 99pps backlog 0b 1000p requeues 0
lended: 340 borrowed: 22060 giants: 0
tokens: -498140 ctokens: 414

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12526920 bytes 8285 pkt (dropped 0, overlimits 0 requeues 0)
rate 510152bit 42pps backlog 0b 0p requeues 0
lended: 8271 borrowed: 14 giants: 0
tokens: -7839 ctokens: 4160

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 68214300 bytes 45125 pkt (dropped 0, overlimits 0 requeues 0)
rate 2679Kbit 221pps backlog 0b 0p requeues 0
lended: 23150 borrowed: 0 giants: 0
tokens: -3610 ctokens: -3610

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1206576 bytes 798 pkt (dropped 0, overlimits 0 requeues 0)
rate 51248bit 4pps backlog 0b 0p requeues 0
lended: 798 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 20628216 bytes 13643 pkt (dropped 0, overlimits 0 requeues 0)
rate 917752bit 76pps backlog 0b 1p requeues 0
lended: 12566 borrowed: 1076 giants: 0
tokens: -3748 ctokens: -953


qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 69900222 bytes 46241 pkt (dropped 45065, overlimits 95950 requeues 0)
rate 0bit 0pps backlog 0b 1000p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 35453880 bytes 23460 pkt (dropped 45084, overlimits 0 requeues 0)
rate 1197Kbit 99pps backlog 0b 898p requeues 0
lended: 342 borrowed: 22220 giants: 0
tokens: -585641 ctokens: 9

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12564720 bytes 8310 pkt (dropped 0, overlimits 0 requeues 0)
rate 511128bit 42pps backlog 0b 0p requeues 0
lended: 8296 borrowed: 14 giants: 0
tokens: 4594 ctokens: 4160

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 68571132 bytes 45361 pkt (dropped 0, overlimits 0 requeues 0)
rate 2680Kbit 222pps backlog 0b 0p requeues 0
lended: 23314 borrowed: 0 giants: 0
tokens: -1007 ctokens: -1007

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1211112 bytes 801 pkt (dropped 0, overlimits 0 requeues 0)
rate 51288bit 4pps backlog 0b 0p requeues 0
lended: 801 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 20696256 bytes 13688 pkt (dropped 0, overlimits 0 requeues 0)
rate 918888bit 76pps backlog 0b 0p requeues 0
lended: 12608 borrowed: 1080 giants: 0
tokens: -7424 ctokens: 4160

qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 69925968 bytes 46259 pkt (dropped 45084, overlimits 96106 requeues 0)
rate 0bit 0pps backlog 0b 787p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 35453880 bytes 23460 pkt (dropped 45084, overlimits 0 requeues 0)
rate 1197Kbit 99pps backlog 0b 666p requeues 0
lended: 343 borrowed: 22451 giants: 0
tokens: -160618 ctokens: 356

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12564720 bytes 8310 pkt (dropped 0, overlimits 0 requeues 0)
rate 511128bit 42pps backlog 0b 0p requeues 0
lended: 8296 borrowed: 14 giants: 0
tokens: 4594 ctokens: 4160

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 68921916 bytes 45593 pkt (dropped 0, overlimits 0 requeues 0)
rate 2680Kbit 222pps backlog 0b 0p requeues 0
lended: 23545 borrowed: 0 giants: 0
tokens: -359 ctokens: -359

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1211112 bytes 801 pkt (dropped 0, overlimits 0 requeues 0)
rate 51288bit 4pps backlog 0b 0p requeues 0
lended: 801 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 20696256 bytes 13688 pkt (dropped 0, overlimits 0 requeues 0)
rate 918888bit 76pps backlog 0b 0p requeues 0
lended: 12608 borrowed: 1080 giants: 0
tokens: -7424 ctokens: 4160

qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 69925968 bytes 46259 pkt (dropped 45084, overlimits 96234 requeues 0)
rate 0bit 0pps backlog 0b 555p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 35453880 bytes 23460 pkt (dropped 45084, overlimits 0 requeues 0)
rate 1197Kbit 99pps backlog 0b 419p requeues 0
lended: 345 borrowed: 22696 giants: 0
tokens: -263712 ctokens: -2145

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12564720 bytes 8310 pkt (dropped 0, overlimits 0 requeues 0)
rate 511128bit 42pps backlog 0b 0p requeues 0
lended: 8296 borrowed: 14 giants: 0
tokens: 4594 ctokens: 4160

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 69295380 bytes 45840 pkt (dropped 0, overlimits 0 requeues 0)
rate 2680Kbit 222pps backlog 0b 0p requeues 0
lended: 23790 borrowed: 0 giants: 0
tokens: -2828 ctokens: -2828

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1211112 bytes 801 pkt (dropped 0, overlimits 0 requeues 0)
rate 51288bit 4pps backlog 0b 0p requeues 0
lended: 801 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 20696256 bytes 13688 pkt (dropped 0, overlimits 0 requeues 0)
rate 918888bit 76pps backlog 0b 0p requeues 0
lended: 12608 borrowed: 1080 giants: 0
tokens: -7424 ctokens: 4160

qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 69984936 bytes 46298 pkt (dropped 45084, overlimits 96392 requeues 0)
rate 0bit 0pps backlog 0b 361p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 35837928 bytes 23714 pkt (dropped 45084, overlimits 0 requeues 0)
rate 1104Kbit 91pps backlog 0b 521p requeues 0
lended: 347 borrowed: 22846 giants: 0
tokens: -370797 ctokens: 4160

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12614616 bytes 8343 pkt (dropped 0, overlimits 0 requeues 0)
rate 415104bit 34pps backlog 0b 0p requeues 0
lended: 8329 borrowed: 14 giants: 0
tokens: -6589 ctokens: 414

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 69665862 bytes 46086 pkt (dropped 0, overlimits 0 requeues 0)
rate 2677Kbit 221pps backlog 0b 0p requeues 0
lended: 23941 borrowed: 0 giants: 0
tokens: -676 ctokens: -676

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1217160 bytes 805 pkt (dropped 0, overlimits 0 requeues 0)
rate 41488bit 3pps backlog 0b 0p requeues 0
lended: 805 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 20782440 bytes 13745 pkt (dropped 0, overlimits 0 requeues 0)
rate 746624bit 62pps backlog 0b 0p requeues 0
lended: 12664 borrowed: 1081 giants: 0
tokens: -10714 ctokens: 3726

qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 70703136 bytes 46773 pkt (dropped 45084, overlimits 96883 requeues 0)
rate 0bit 0pps backlog 0b 606p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 36371664 bytes 24067 pkt (dropped 45084, overlimits 0 requeues 0)
rate 1104Kbit 91pps backlog 0b 769p requeues 0
lended: 349 borrowed: 22949 giants: 0
tokens: -535265 ctokens: 4160

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12679632 bytes 8386 pkt (dropped 0, overlimits 0 requeues 0)
rate 415104bit 34pps backlog 0b 0p requeues 0
lended: 8372 borrowed: 14 giants: 0
tokens: 4594 ctokens: 4160

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 70018158 bytes 46319 pkt (dropped 0, overlimits 0 requeues 0)
rate 2677Kbit 221pps backlog 0b 0p requeues 0
lended: 24048 borrowed: 0 giants: 0
tokens: -3269 ctokens: -3269

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1223208 bytes 809 pkt (dropped 0, overlimits 0 requeues 0)
rate 41488bit 3pps backlog 0b 0p requeues 0
lended: 809 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 20904912 bytes 13826 pkt (dropped 0, overlimits 0 requeues 0)
rate 746624bit 62pps backlog 0b 0p requeues 0
lended: 12741 borrowed: 1085 giants: 0
tokens: -5046 ctokens: 4160

qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 71439480 bytes 47260 pkt (dropped 45084, overlimits 97393 requeues 0)
rate 0bit 0pps backlog 0b 860p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 36879696 bytes 24403 pkt (dropped 45107, overlimits 0 requeues 0)
rate 1104Kbit 91pps backlog 0b 1000p requeues 0
lended: 350 borrowed: 23053 giants: 0
tokens: -111329 ctokens: -594

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12747672 bytes 8431 pkt (dropped 0, overlimits 0 requeues 0)
rate 415104bit 34pps backlog 0b 0p requeues 0
lended: 8417 borrowed: 14 giants: 0
tokens: -1908 ctokens: 4160

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 70373478 bytes 46554 pkt (dropped 0, overlimits 0 requeues 0)
rate 2677Kbit 221pps backlog 0b 0p requeues 0
lended: 24161 borrowed: 0 giants: 0
tokens: -12974 ctokens: -12974

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1230768 bytes 814 pkt (dropped 0, overlimits 0 requeues 0)
rate 41488bit 3pps backlog 0b 0p requeues 0
lended: 814 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 21027384 bytes 13907 pkt (dropped 0, overlimits 0 requeues 0)
rate 746624bit 62pps backlog 0b 1p requeues 0
lended: 12812 borrowed: 1094 giants: 0
tokens: -11292 ctokens: 968

qdisc htb 9997: root r2q 10 default 9999 direct_packets_stat 0
Sent 71998920 bytes 47630 pkt (dropped 45192, overlimits 97894 requeues 0)
rate 0bit 0pps backlog 0b 1000p requeues 0
class htb 9997:9999 parent 9997:9998 prio 2 rate 20000bit ceil 2700Kbit burst 1609b cburst 2949b
Sent 37035432 bytes 24506 pkt (dropped 45354, overlimits 0 requeues 0)
rate 1104Kbit 91pps backlog 0b 1000p requeues 0
lended: 352 borrowed: 23154 giants: 0
tokens: -280899 ctokens: -162

class htb 9997:1 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 12814200 bytes 8475 pkt (dropped 0, overlimits 0 requeues 0)
rate 415104bit 34pps backlog 0b 0p requeues 0
lended: 8461 borrowed: 14 giants: 0
tokens: -2745 ctokens: 4160

class htb 9997:9998 root rate 2700Kbit ceil 2700Kbit burst 2949b cburst 2949b
Sent 70722792 bytes 46786 pkt (dropped 0, overlimits 0 requeues 0)
rate 2677Kbit 221pps backlog 0b 0p requeues 0
lended: 24272 borrowed: 0 giants: 0
tokens: -7053 ctokens: -7053

class htb 9997:2 parent 9997:9998 prio 0 rate 100000bit ceil 2700Kbit burst 1649b cburst 2949b
Sent 1236816 bytes 818 pkt (dropped 0, overlimits 0 requeues 0)
rate 41488bit 3pps backlog 0b 0p requeues 0
lended: 818 borrowed: 0 giants: 0
tokens: 10781 ctokens: 4160

class htb 9997:3 parent 9997:9998 prio 0 rate 1000Kbit ceil 2700Kbit burst 2099b cburst 2949b
Sent 21145320 bytes 13985 pkt (dropped 0, overlimits 0 requeues 0)
rate 746624bit 62pps backlog 0b 0p requeues 0
lended: 12883 borrowed: 1102 giants: 0
tokens: 4594 ctokens: 4160

I added SFQ beneath the classes, as described in Section 9.5.5.1 on page 65 of the Linux Advanced Routing & Traffic Control HOWTO (Version 1.43), and have not seen the problem occur again. I watched it for 30 minutes. I was seeing it happen in a few minutes. I will continue to test to verify it is gone, but this looks promising.