Performance Analysis of Greedy Shapers in Real-Time Systems
Computer Engineering and Networks Laboratory
Swiss Federal Institute of Technology (ETH)
8092 Z¨ urich, Switzerland
Alexander MaxiaguineLothar Thiele
Abstract— Traffic shaping is a well-known technique in the
area of networking and is proven to reduce global buffer require-
ments and end-to-end delays in networked systems. Due to these
properties, shapers also play an increasingly important role in the
design of multi-processor embedded systems that exhibit a consid-
erable amount of on-chip traffic. Despite their growing importance
in this area, no methods exist to analyze shapers in distributed em-
bedded systems, and to incorporate them into a system-level per-
formance analysis. Hence it is until now not possible to determine
the effect of shapers to end-to-end delay guarantees or buffer re-
quirements in these systems. In this work, we present a method to
analyze greedy shapers, and we embed this analysis method into
a well-established modular performance analysis framework. The
presented approach enables system-level performance analysis of
complete systems with greedy shapers, and we prove its applica-
bility by analyzing two case study systems.
In the area of broad-band networking, traffic shaping is
a well-known and well-studied technique to regulate con-
nections and to avoid buffer overflow in network nodes, see
e.g.  or . A traffic shaper in a network node buffers the
data packets of an incoming traffic stream and delays them
such that the output stream conformsto a given traffic spec-
ification. A shaper may ensure for example that the output
stream has limited burstiness, or that packets on the out-
put stream have a specified minimum inter-arrival time. A
greedy shaper is a special instance of a traffic shaper, that
not only ensures an output stream stream that conforms to
a given traffic specification, but that also guarantees that no
packets get delayed any longer than necessary.
By limiting the burstiness of the output stream of a net-
work node, shapers typically drastically reduce the buffer
requirements on subsequent network nodes. And if some
sort of priority scheduling is used on a network node to
share bandwidth among several incoming streams, then a
limitedburstiness of high-prioritystreams leads to betterre-
sponsiveness of lower-priority streams.
In addition, under some circumstances, shaping comes
for free from a performance point of view. To be more spe-
cific, if the output stream of a node is shaped with a greedy
shaper to conform again to the input traffic specification,
and if the buffer of the shaper accesses the same memory
as the input buffer of the node, then the end-to-end delay
of the stream and the total buffer requirements on the net-
work node are not affected by adding the shaper.
Due to these favorable properties, shapers also play an
increasingly important role in the design of real-time em-
bedded systems. Particularly, since modern embedded sys-
tems are often implemented as multi-processor systems
with a considerable amount of on-chip traffic.
In this domain,we may identifytwo main applicationar-
eas fortraffic shaping.First, shapers maybe used internally,
to re-shape internal traffic streams to reduce global buffer
requirements and end-to-end delays, and secondly, shapers
may be added at the boundaries of a system, to ensure con-
formantinput streams and to thereby preventinternal buffer
overflows caused by malicious input. Figure 1 shows two
simple example systems from these two application areas.
Figure 1. Two systems with greedy shapers.
The analysis of traffic shapers in communication net-
works is well-known . But to our best knowledge, none
of the existing frameworks for modular system level per-
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