Date:	Thu, 20 Mar 2008 11:51:00 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Djalel Chefrour <cdjalel@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Does HTB traffic shaping happen on leaf classes only or could
	it happen at root qdisc

On 18-03-2008 13:39, Djalel Chefrour wrote:
> Hi
> 
> According to Traffic-Control-HOWTO
> (http://tldp.org/HOWTO/Traffic-Control-HOWTO/classful-qdiscs.html),
> with HTB scheduler, traffic is only throttled in leaf classes.
> I wonder if this is true in recent implementations ?
> 
> In the log below, with kernel 2.6.12.6, "overlimits" increases only
> for "root qdisc",
> While uplink rate is 256kbs and I am sending 100kbps to high prio class 1:110
> and doing ftp upload through class 1:20.
> 
> # tc -s -d qdisc show dev ppp0
> qdisc htb 1: r2q 10 default 20 direct_packets_stat 2 ver 3.17
>  Sent 8926254 bytes 23133 pkts (dropped 0, overlimits 37101 )
>  backlog 82p
> qdisc pfifo 110: parent 1:110 limit 50p
>  Sent 3887561 bytes 19364 pkts (dropped 0, overlimits 0 )
> qdisc pfifo 120: parent 1:120 limit 50p
>  Sent 0 bytes 0 pkts (dropped 0, overlimits 0 )
> qdisc sfq 20: parent 1:20 limit 128p quantum 1492b flows 128/1024 perturb 10sec
>  Sent 5037436 bytes 3767 pkts (dropped 0, overlimits 0 )
>  backlog 82p
> 
> # tc -s -d class show dev ppp0
> class htb 1:110 parent 1:10 leaf 110: prio 0 quantum 1375 rate 110Kbit
> ceil 220Kbit burst 323b/2 mpu 0b overhead 18b atm cburst 392b/2 mpu 0b

Are these default quantum, burst and cburst parameters?

> overhead 18b atm level 0
>  Sent 3888361 bytes 19368 pkts (dropped 0, overlimits 0)
>  rate 7160bit 35pps
>  lended: 19348 borrowed: 20 giants: 50

giants (>mtu) means something goes out of band here.

>  tokens: 2404 ctokens: 3813
> 
> class htb 1:1 root rate 256Kbit ceil 256Kbit burst 1760b/8 mpu 0b
> overhead 18b atm cburst 1760b/8 mpu 0b overhead 18b atm level 7
>  Sent 8806437 bytes 23055 pkts (dropped 0, overlimits 0)
>  rate 26913bit 49pps
>  lended: 2365 borrowed: 0 giants: 0
>  tokens: -86236 ctokens: -86236
> 
> class htb 1:10 parent 1:1 rate 210Kbit ceil 256Kbit burst 1730b/8 mpu
> 0b overhead 18b atm cburst 1760b/8 mpu 0b overhead 18b atm level 6
>  Sent 3888361 bytes 19368 pkts (dropped 0, overlimits 0)
>  rate 7279bit 36pps
>  lended: 20 borrowed: 0 giants: 0
>  tokens: 45750 ctokens: 38273
> 
> class htb 1:20 parent 1:1 leaf 20: prio 7 quantum 1500 rate 46Kbit
> ceil 256Kbit burst 1627b/8 mpu 0b overhead 18b atm cburst 1760b/8 mpu
> 0b overhead 18b atm level 0
>  Sent 5038928 bytes 3768 pkts (dropped 0, overlimits 0)
>  rate 160Kbit 13pps backlog 81p
>  lended: 1322 borrowed: 2365 giants: 0
>  tokens: -154108 ctokens: -41778
> 
> class htb 1:120 parent 1:10 leaf 120: prio 1 quantum 1250 rate 100Kbit
> ceil 100Kbit burst 317b/2 mpu 0b overhead 18b atm cburst 317b/2 mpu 0b
> overhead 18b atm level 0
>  Sent 0 bytes 0 pkts (dropped 0, overlimits 0)
>  lended: 0 borrowed: 0 giants: 0
>  tokens: 20840 ctokens: 20840
> 
> 
> Normally traffic sent to 1:110 should not be delayed, but I am
> experiencing an important latency there,
> also traffic going 1:20 should is not dropped as one would expect !!!

Looks like all is within (below) rates, so no need to drop. Latency
could be caused by various reasons, mainly wrong parameters. Usually
defaults are reasonable with normal size packets. But these questions
aren't the preferred subject of this list...

> Does this mean traffic is shaped at the root qdisc before it is
> classified and sent down ?

No, HTB root qdisc doesn't even have parameter for shaping.
BTW, did you read this fine manual?:
http://luxik.cdi.cz/~devik/qos/htb/manual/userg.htm

Regards,
Jarek P.
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