Give a brief introduction on the internals on htb. How link sharing works etc

1. htb
Jeromy Fu

2. Agenda
• Parameters
• Tc example
• Link sharing
• Implementation
• Case study

3. Tc Parameters

4. Internal Parameters

5. example1

6. example1

7. example1

8. example2

9. example2

10. example2

11. Basic concepts
• Classful qdisc
• Assured rate(AR)
• Ceil rate(CR)
• Actual rate(R)
• Priority
• Quantum, DRR

12. Basic concepts
• Class mode
HTB_CANT_SEND: red, R>CR
HTB_MAY_BORROW: yellow, AR<R<=CR
HTB_CAN_SEND: green, R<=AR

13. Link sharing
• Rc = min(CRc, ARc+Bc)
- Rc, actual Rate of class c
- CRc, Ceil Rate of class c
- ARc, Assured Rate of class c
- Bc, Borrowed from parent class c
• D(p) – set of nodes
- all nodes are children of p
- all nodes are yellow, which need to borrow bandwidth from parent p

14. Link sharing
• If there are other nodes have higher priority than node c, then those ones
will be scheduled first, thus Bc = 0.
• Otherwise, the bandwidth of parent is divided according to the quantum
of the nodes, which have the same priority with node c.
- Q, quantum
- P, Priority, smaller the higher
- Rp, actual rate of parent p
if min[Pi over D(p)] >= Pc:
Bc = Qc * Rp/sum[Qi over D(p) where Pi=Pc]
else:
Bc = 0

15. Principles
• Red nodes(HTB_CANT_SEND) have to wait
• Yellow nodes(HTB_MAY_BORROW) will try
borrow from parent
• Green nodes(HTB_CAN_SEND) will always
served first for it doesn’t borrow
• Higher priority nodes are served first

16. implementation
• Self feed
each level has one self feed, and every priority has a self slot in self feed(each
slot has the same priority and level).
All classes in the same slot has the same priority and level, and are all green
nodes (HTB_CAN_SEND) of this level.
• Inner feed
every inner class(node) has one inner feed
All classes in the same slot has the same priority and level, and are all yellow
nodes (HTB_MAY_BORROW) that are children of current inner node.
• Wait list
each level has one wait list, which stores the nodes that are yellow
(HTB_MAY_BORROW) and red (HTB_CANT_SENT)

17. implementation
• A htb tree with 3 levels
- red slot (high priority)
- blue slot (lower priority)
- white slot (wait list)

18. implementation
• Start at the lowest level, choose one green
node in the highest priority self slot of this self
feed.
• If it’s leaf, then schedule it.
• If it’s inner node, then check its inner
feed, and choose the highest priority inner
slot, find a yellow node, then schedule it.

19. Case study
• All nodes are initially green
• Pkt arrived for C and D (thick circle)
• C is lower priority (in blue self slot)
• D is higher priority (in red self slot)
• D is scheduled and token is
used

20. Case study
• D exceed AR, but not CR
• D changed to yellow
• D is removed from self slot(red) of level 0
• D is then put to inner slot(red) of B
• D will change back to green in
the future, so it also put into
wait list of level 0
• C is scheduled ( D is higher
priority but C doesn’t need
borrow)

21. Case study
• C exceed CR
• C changed to red
• C is removed from self slot(blue) of level 0
• C can’t borrow so it won’t be put to the parent inner slot
• C will change back to green in
the future, so it also put into
wait list of level 0
• D is scheduled, and borrowed
from B, and B changed to yellow
• B is removed from self slot(red) of
level 1
• B is put to the parent inner slot(red)
and also put to the wait list
• Only A and E are green now

22. Case study
• E has no pkt, so D is scheduled
• A changed to red
• A is removed from self slot(red) of level 2
• A is put to wait list of level2
• Pkt arrived for E (thick circle)
• E is green and lower priority,
so put to self slot(blue) of level 0
• C changed back to green, and
removed from wait list, and put
to self slot(blue) of level 0

23. Case study
• Now both C and E are green and are of the
same priority.
• DRR is used now, they’re scheduled according
to quantum.
• Both C and D are changed to
yellow, removed from self slot,
put to inner slot and wait list
• B is added to both high and
lower priority inner slot of A