сегмент токенов иерархии (Hierarchy Token Bucket)
Имя (Name)
HTB - Hierarchy Token Bucket
Синопсис (Synopsis)
tc qdisc ... dev dev ( parent classid | root) [ handle major: ]
htb [ default minor-id ] [ r2q divisor ] [ offload ]
tc class ... dev dev parent major:[minor] [ classid major:minor ]
htb rate rate [ ceil rate ] burst bytes [ cburst bytes ] [ prio
priority ] [ quantum bytes ]
Описание (Description)
HTB is meant as a more understandable and intuitive replacement
for the CBQ qdisc in Linux. Both CBQ and HTB help you to control
the use of the outbound bandwidth on a given link. Both allow you
to use one physical link to simulate several slower links and to
send different kinds of traffic on different simulated links. In
both cases, you have to specify how to divide the physical link
into simulated links and how to decide which simulated link to
use for a given packet to be sent.
Unlike CBQ, HTB shapes traffic based on the Token Bucket Filter
algorithm which does not depend on interface characteristics and
so does not need to know the underlying bandwidth of the outgoing
interface.
Алгоритм формирования (Shaping algorithm)
Shaping works as documented in tc-tbf(8).
Классификация (Classification)
Within the one HTB instance many classes may exist. Each of these
classes contains another qdisc, by default tc-pfifo(8).
When enqueueing a packet, HTB starts at the root and uses various
methods to determine which class should receive the data.
In the absence of uncommon configuration options, the process is
rather easy. At each node we look for an instruction, and then
go to the class the instruction refers us to. If the class found
is a barren leaf-node (without children), we enqueue the packet
there. If it is not yet a leaf node, we do the whole thing over
again starting from that node.
The following actions are performed, in order at each node we
visit, until one sends us to another node, or terminates the
process.
(i) Consult filters attached to the class. If sent to a
leafnode, we are done. Otherwise, restart.
(ii) If none of the above returned with an instruction, enqueue
at this node.
This algorithm makes sure that a packet always ends up somewhere,
even while you are busy building your configuration.
Алгоритм обмена ссылкой (Link sharing algorithm)
FIXME
Диск очереди, основанной на классах (QDISC)
The root of a HTB qdisc class tree has the following parameters:
parent major:minor | root
This mandatory parameter determines the place of the HTB
instance, either at the root of an interface or within an
existing class.
handle major:
Like all other qdiscs, the HTB can be assigned a handle.
Should consist only of a major number, followed by a
colon. Optional, but very useful if classes will be
generated within this qdisc.
default minor-id
Unclassified traffic gets sent to the class with this
minor-id.
r2q divisor
Divisor used to calculate quantum values for classes.
Classes divide rate by this number. Default value is 10.
offload
Offload the HTB algorithm to hardware (requires driver and
device support).
Классы (Classes)
Classes have a host of parameters to configure their operation.
parent major:minor
Place of this class within the hierarchy. If attached
directly to a qdisc and not to another class, minor can be
omitted. Mandatory.
classid major:minor
Like qdiscs, classes can be named. The major number must
be equal to the major number of the qdisc to which it
belongs. Optional, but needed if this class is going to
have children.
prio priority
In the round-robin process, classes with the lowest
priority field are tried for packets first.
rate rate
Maximum rate this class and all its children are
guaranteed. Mandatory.
ceil rate
Maximum rate at which a class can send, if its parent has
bandwidth to spare. Defaults to the configured rate,
which implies no borrowing
burst bytes
Amount of bytes that can be burst at ceil speed, in excess
of the configured rate. Should be at least as high as the
highest burst of all children.
cburst bytes
Amount of bytes that can be burst at 'infinite' speed, in
other words, as fast as the interface can transmit them.
For perfect evening out, should be equal to at most one
average packet. Should be at least as high as the highest
cburst of all children.
quantum bytes
Number of bytes to serve from this class before the
scheduler moves to the next class. Default value is rate
divided by the qdisc r2q parameter. If specified, r2q is
ignored.
Примечание (Note)
Due to Unix timing constraints, the maximum ceil rate is not
infinite and may in fact be quite low. On Intel, there are 100
timer events per second, the maximum rate is that rate at which
'burst' bytes are sent each timer tick. From this, the minimum
burst size for a specified rate can be calculated. For i386, a
10mbit rate requires a 12 kilobyte burst as 100*12kb*8 equals
10mbit.
Смотри также (See also)
tc(8)
HTB website: http://luxik.cdi.cz/~devik/qos/htb/
