Authors: Jeffrey M. Wagner 、 Weirong Jiang 、 Viktor K. Prasanna

Conf. : International Conference on Parallel and Distributed Computing and Systems (PDCS '09)

Presenter : JHAO-YAN JIANDate : 2010/10/20

A SCALABLE PIPELINE ARCHITECTURE FOR LINE RATE

PACKET CLASSIFICATION ON FPGAS

OutlineIntroductionMemory balancing and waste reduction

Tree partitioning and subtree inversionBidirectional fine-grained mappingConfigurable rule list mapping

Hardware architecture implementationExperimental results

Introduction(1/2)due to the rapid growth of the rule set size and the

current link rate having been pushed beyond the OC-768 rate, i.e. 40 Gbps.such throughput is impossible using existing software-

based solutionsPipelining approach for decision treeIn an unbalanced pipeline, the “fattest” stage, which

stores the largest number of tree nodes / rules.More time is needed to access the pipeline stages

containing larger local memoryneed to allocate memory with the maximum size for

each stage. Such overprovisioning results in memory wastage and excessive power consumption.

Introduction(2/2)State-of-the-art techniques cannot achieve

perfectly balanced memory distribution: 1. They require the tree nodes on the same level be mapped

onto the same stage.(Fine-grained mapping) 2. Their mapping scheme is uni-directional: the subtrees

partitioned from the original tree must be mapped in the same.(Bidirectional mapping)

Fine-grained mapping : If node A is an ancestor of node B in a tree, then A must

be mapped to a stage preceding the stage to which B is mapped.

Tree partitioning and subtree inversion Inverted : Based on Largestleaf heuristic, select S with the most

number of leaves from those not inverted. And then W = W− (nodesize of S root node) +(# of leaves of S) W :total nodesize of all subtree root nodes 、 CAP :ideal stage

capacity 、 IFR :inversion factor 、 S :subtrees

Selection end : W >= (IFR × CAP)

Bidirectional fine-grained mapping Decision tree mapping utilizes the two sets of subtrees which are

mapped from roots are called the forward subtrees, while the others are called the reverse subtrees.

It manage two lists, ReadyList and NextReadyList. Initial: Push the roots of forward subtrees and the leaves of reverse

subtrees into ReadyList. Mi :the memory address pointer for stage i.

Configurable rule list mapping

The configurable mapping algorithm maps the rule lists to a second independent pipeline.

Fine-grained mapping

Configurable rule list mapping

Sort the rule lists in ReadyList in decreasing order of ruledepth. Dual-port mapping: allows a rule list to map its rules vertically

within a single pipeline stage memory by occupying two consecutive memory addresses.

Variable-width mapping :allows a rule list to map its rules horizontally within a single pipeline stage

Hardware architecture implementation

Direction Index Table (DIT) outputs: (1) the distance to the stage where the subtree root is stored in the

decision tree pipeline (2) the memory address of the root in that stage (3) the mapping direction which leads the packet to the

different entrances of the decision tree pipeline.

Bidirectional pipeline(1/2) The decision tree pipeline stage memory is constructed using a

dual-port synchronous read RAM.

Bidirectional pipeline(2/2)Cut logic:

propose a circuit design using left and right shifters.To generate the next node pointer, the MSB bits of

the packet fields, number of cuts on each field, and a base address are used.

Distance checker:allows two nodes on the same tree level to be

mapped to different stages.storing the distance to the pipeline stage where the

child node is stored in the local pipeline stage memory.

When the distance value becomes 0, the child node’s address is used to access the memory in that stage.

Configurable pipeline(1/2) The rule list pipeline stage memory is configurable based on

memory port and width configurations.

Configurable pipeline(2/2)Rule match and compare logic

If memory port and width configurations are utilized, multiple rules can be retrieved in a single stage.

Rule checkersimilar to the bidirectional pipeline distance checkerThe rule count field stores the distance to the

pipeline stage where the end of the rule list is.

Experimental results(1/2)

Experimental results(2/2)