OpenFlow is unable to provide customized flow tables, resulting in memory explosions and high switch retirement rates. This is the bottleneck for the development of SDN. Recently, P4 (Programming Protocol-independent Packet Processors) attracts much attentions from both academia and industry. It provides customized networking services by offering flow-level control. P4 can “produce” various forwarding tables according to packets. P4 increases the speed of custom ASICs. However, with the prevalence of P4, the multiple forwarding tables could explode when used in large scale networks. The explosion problem can slow down the lookup speed, which causes congestions and packet losses. In addition, the pipelined structure of forwarding tables brings additional processing delay. In this study, we will improve the lookup performance by optimizing the forwarding tables of P4. Intuitively, we will install the rules according to their popularity, i.e., the popular rules will appear earlier than others. Thus, the packets can hit the matched rule sooner. In this paper, we formalize the optimization problem, and prove that the problem is NP-hard. To solve the problem, we propose a heuristic algorithm called EPSP (Efficient Pipeline Processing Scheme for P4), which can largely reduce the lookup time while keeping the forwarding actions the same. Because running the optimization algorithm frequently brings additional processing burdens, wedesign an incremental update algorithm to alleviate this problem. To evaluate the proposed algorithms, we set up the simulation environments based on ns-3. The simulation results show that the algorithm greatly reduces both the lookup time and the number of memory accesses. The incremental algorithm largely reduces the processing burdens while the lookup time remains almost the same with the non-incremental algorithm. We also implemented a prototype using floodlight and mininet. The results show that our algorithm brings acceptable burder, and performs better than traditional algorithm.

OpenFlow无法提供自定义的流表，从而导致内存爆炸和高交换机报废率。这是SDN发展的瓶颈。最近，P4（与编程协议无关的分组处理器）引起了学术界和工业界的广泛关注。它通过提供流级别控制来提供定制的网络服务。P4可以根据数据包“生成”各种转发表。P4提高了定制ASIC的速度。但是，随着P4的普及，在大型网络中使用时，多个转发表可能会爆炸。爆炸问题可能会减慢查找速度，从而导致拥塞和数据包丢失。另外，转发表的流水线结构带来额外的处理延迟。在这个研究中，我们将通过优化P4的转发表来提高查找性能。直观上，我们将根据规则的流行程度来安装它们，即流行规则的出现时间将比其他规则早。因此，数据包可以更快地达到匹配的规则。在本文中，我们将优化问题形式化，并证明该问题是NP难的。为了解决这个问题，我们提出了一种启发式算法，称为EPSP（Ë fficient P ipeline处理小号cheme为P4），这可以大大减少查找时间，同时保持转发操作不变。由于运行优化算法经常会带来额外的处理负担，因此我们设计了增量更新算法来缓解此问题。为了评估提出的算法，我们建立了基于ns-3的仿真环境。仿真结果表明，该算法大大减少了查找时间，减少了内存访问次数。增量算法大大减少了处理负担，而查找时间与非增量算法几乎保持不变。我们还使用Floodlight和Mininet实现了一个原型。结果表明，该算法带来了可接受的毛刺，并且性能优于传统算法。