Hello folks, I observe unused bandwidth on my QoS policy that I cannot explain. Conditions are: I have a HTB tree with 8 classes and a total rate of 768kbits. I use the ATM option so I assume the real rate to be something close to 675kbits (about 88% of the ethernet rate). The sum of my 8 rates is exactly 768kbits. Some have ceil values up to 768kbits. When class 20 "tcp_acks" starts borrowing, TC reduces the total bandwidth down to 595kbits/S (minus 79kbits/s). And I can't explain why.... The attached graph "tc_htb_weirdness.png" shows the result: there are 'holes' in the sending rate. I tried to play with burst sizes, r2q value and hysteresis mode, but the results are the same. System is debian squeeze, kernel version is 2.6.26, iproute2 version is 2.6.26 - 07/25/2008. I have attached two files: - "tcrules.txt" : the traffic control rules - "tc_htb_weirdness.png" : the rrdtool graph, resolution is 1 second. And here: http://jve.linuxwall.info/ressources/code/tc_hole_analysis.html a sheet with some of the measures values. I used it to calculate the size of one of the hole. The last table (with green and red cells) shows that, when class 20 "tcp_acks" starts sending at unixtime 1265496813, there is a lot of bandwidth left over (last column is all green). During the 95 seconds while class 20 is sending, 3880776 bits could be sent but are not. That's about 40kbits/s on average. Does anybody observess the same behavior? Any logical explanation to this or is it a bug ? Julien
#root tc qdisc add dev eth0 root handle 1: htb default 99 r2q 100 #main branch tc class add dev eth0 parent 1:0 classid 1:1 htb rate 768kbit ceil 768kbit linklayer atm overhead 5 # class 10 "interactive" tc class add dev eth0 parent 1:1 classid 1:10 htb rate 128kbit ceil 200kbit burst 5k prio 1 linklayer atm overhead 5 tc qdisc add dev eth0 parent 1:10 handle 110: pfifo limit 1000 tc filter add dev eth0 parent 1:0 protocol ip prio 1 handle 10 fw flowid 1:10 # class 20 "tcp_acks" tc class add dev eth0 parent 1:1 classid 1:20 htb rate 64kbit ceil 768kbit burst 3k prio 2 linklayer atm overhead 5 tc qdisc add dev eth0 parent 1:20 handle 120: pfifo limit 1000 tc filter add dev eth0 parent 1:0 protocol ip prio 2 handle 20 fw flowid 1:20 # class 30 "ssh" tc class add dev eth0 parent 1:1 classid 1:30 htb rate 64kbit ceil 300kbit burst 2k prio 3 linklayer atm overhead 5 tc qdisc add dev eth0 parent 1:30 handle 130: sfq perturb 10 tc filter add dev eth0 parent 1:0 protocol ip prio 3 handle 30 fw flowid 1:30 # class 40 "main web" tc class add dev eth0 parent 1:1 classid 1:40 htb rate 256kbit ceil 768kbit burst 20k prio 4 linklayer atm overhead 5 # class 41 "sub web 1" tc class add dev eth0 parent 1:40 classid 1:41 htb rate 100kbit ceil 768kbit burst 20k prio 4 linklayer atm overhead 5 tc qdisc add dev eth0 parent 1:41 handle 141: sfq perturb 10 tc filter add dev eth0 parent 1:0 protocol ip prio 4 handle 41 fw flowid 1:41 # class 42 "sub web 2" tc class add dev eth0 parent 1:40 classid 1:42 htb rate 100kbit ceil 768kbit burst 20k prio 4 linklayer atm overhead 5 tc qdisc add dev eth0 parent 1:42 handle 142: sfq perturb 10 tc filter add dev eth0 parent 1:0 protocol ip prio 5 handle 42 fw flowid 1:42 # class 49 "sub web gen" tc class add dev eth0 parent 1:40 classid 1:49 htb rate 56kbit ceil 768kbit burst 20k prio 4 linklayer atm overhead 5 tc qdisc add dev eth0 parent 1:49 handle 149: sfq perturb 10 tc filter add dev eth0 parent 1:0 protocol ip prio 6 handle 49 fw flowid 1:49 # class 50 "torrent" tc class add dev eth0 parent 1:1 classid 1:50 htb rate 128kbit ceil 768kbit burst 2k prio 5 linklayer atm overhead 5 tc qdisc add dev eth0 parent 1:50 handle 150: sfq perturb 10 tc filter add dev eth0 parent 1:0 protocol ip prio 7 handle 50 fw flowid 1:50 # class 99 "default" tc class add dev eth0 parent 1:1 classid 1:99 htb rate 128kbit ceil 768kbit burst 2k prio 5 linklayer atm overhead 5 mtu 1500 tc qdisc add dev eth0 parent 1:99 handle 199: sfq perturb 10 tc filter add dev eth0 parent 1:0 protocol ip prio 99 handle 99 fw flowid 1:99
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tc_htb_weirdness.png
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