Greetings,
: now, i'm learning and try to read a lot of article about tc
: command in linux for setting traffic shaper. but i'm doubt about
: In the theory about tc command ... In general, we define class
: under root qdisc but Is it can be possible ???? If we define
: another qdisc under root qdisc, Can i do it? because i have just
: read tc command syntax and i found this point ...
[ snip mangled "tc qdisc help" output ]
: from above syntax at [handle][root /ingress/ ****parent CLASSID]
: Is "parent CLASSID" mean we can define qdisc under class???? so
: this is my assumption about that. and Could you advise me about
: Is it can do for real????
If I understand your question correctly, the answer is "yes". It is
possible to have nested qdiscs. Note that you can nest qdiscs if
you are using a classful qdisc [0]. See also my list at the bottom
of this message.
: //first .. define root qdisc
:
: tc qdisc add dev eth0 root handle 1: fifo
Bzzzt! Sadly, you can't do this. A fifo qdisc is a classless
qdisc, meaning that it cannot have any children. (Poor barren
thing!)
: //second ... define class under root qdisc but algorithm's not same like root qdisc algorithm
:
: tc class add dev eth0 parent 1: classid 1:1 htb rate 100kbps ceil 100kbps
: tc class add dev eth0 parent 1: classid 1:2 hfsc rate 100kbps ceil 100kbps
Well, you can't quite mix and match classes without having a parent
qdisc of the type you want. An HTB parent qdisc can have any number
of children arranged in a tree structure below the parent.
Similarly, an HFSC class structure needs to attach to an HFSC qdisc
itself. Note, though, you cannot simply change the class name from
htb to hfsc and supply the same parameters. HTB uses the rate and
ceil parameters, but HFSC uses different parameters (rt, sc and ul).
: //later attach qdisc to those classes
:
: tc qdisc add dev eth0 parent 1:1 classid 10:11 htb rate 100kbps ceil 100kbps
: tc qdisc add dev eth0 parent 1:2 classid 10:21 hfsc rate 100kbps ceil 100kbps
OK, now, let's pretend that you have a classful qdisc (e.g. HTB)
with two classes, 1:1 and 1:2, AND that you have a good reason for
adding a nested qdisc to one of these classes. If that were the
case, then you could add the qdiscs to the parent classes in the
following fashion:
# -- create a new qdisc, attached inside an existing class
# hierarchy below class 1:1
#
$qdisc_add parent 1:1 handle 10:0 htb
#
# -- add a class to our newly created qdisc, and set the
# rate and ceil parameters
#
$class_add parent 10:0 classid 10:1 htb rate 100kbps ceil 100kbps
Note, that you'd still need filters.
If I were you, I'd review the documentation for both HTB and HFSC
after understanding the entire Linux traffic control model. Here's
a crash course, starting at the root qdisc:
1. The qdisc can be
- classless (e.g., FIFO, SFQ, ESFQ, TBF, GRED)
- classful (e.g., HTB, HFSC, CBQ, PRIO)
2. If the qdisc is classful, keep reading. If the root qdisc is
classless, stop here.
3. You may add classes to your classful qdisc. If your qdisc is
HTB, you can only add HTB classes. If your qdisc is CBQ, you
can only add CBQ classes. If your qdisc is HFSC...
4. Now, you may attach a brand-new classful or classless qdisc to
one of your existing classes. Repeat from step 1 for each new
qdisc.
5. You may add filters to any of your classes (best starting
behaviour is to add them to 1:0)
Very complex hierarchies are quite possible, even if not always
understandable or advisable.
Best of luck,
-Martin
[0] http://tldp.org/HOWTO/Traffic-Control-HOWTO/classful-qdiscs.html
(N.B., this documentation was written without any reference to
HFSC, a newer classful qdisc. You may also use HFSC with
child qdiscs.)
--
Martin A. Brown
http://linux-ip.net/
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