LWIP中零拷贝技术的研究与应用

Research and Application of Zero Copy Technology in LWIP

LWIP是一种轻量级的TCP/IP协议栈。在运行过程中占用少量的资源,主要应用在低端的嵌入式系统。文中从物理层到应用层,分三个层次分析了LWIP协议栈的数据传递过程。分别是物理层到协议栈内部的数据传递过程、协议栈内部本身的数据传递过程、协议栈和外部应用程序数据的传递过程。而数据在协议栈内部传递时,通过pbuf缓冲包在各层之间传递数据包的地址指针已经实现了数据在协议栈内部各层之间的零拷贝传递。提出了在物理网卡和LWIP协议栈传递数据、外部应用程序和LWIP协议栈传递数据时的改进方法,避免了数据的两次拷贝,从而实现了数据从物理层直达应用层,提高了系统的传输效率和并发性能。测试结果表明,数据传输速率从未优化的2.04 MB/s提升到9.8 MB/s,已接近网卡性能极限。

LWIP,a lightweight TCP/IP stack,occupies a small amount of resources during the operation and is mainly used in low-end embedded systems.From the physical layer to the application layer,the data transfer process of the LWIP protocol stack is analyzed in three levels which are the data transfer process from the physical layer to the protocol stack,the data transfer process inside the protocol stack,and the data transfer between the protocol stack and the external application program. When the data is passed inside the protocol stack,the address pointer of the data packet is transmitted between the layers through the pbuf buffer packet,and the data has been transmitted by zero copy between the layers of the protocol stack.We propose an improved method to transfer data between the physical network card and the LWIP protocol stack,the external application program and the LWIP protocol stack,so as to avoid the two copy of the data.The system realizes the direct application of data from the physical layer to the application layer,and improves the transmission efficiency and the concurrent performance of the system.Test shows that the rate of data transmission has been optimized from 2.04 MB/s to9.8 MB/s,which is close to the network card performance limit.