Page-Flip Technology for use within the Linux Networking Stack
Today's received network data is copied from kernel-space to user-space once the protocol headers have been processed. What is needed is to provide a hardware (NIC) to user-space zero-copy path. This paper discusses a pageflip technique where a page is flipped from kernel memory into user-space via page-table manipulation. Gigabit Ethernet was used to produce this zero-copy receive path within the Linux stack which can then be extrapolated to 10 Gigabit Ethernet environments where the need is more critical. Prior experience in the industry with page-flip methodologies is cited.
The performance of the stack and the overall system is presented along with the testing methodology and tools used to generate the performance data. All data was collected using a modified TCP/IP stack in a 2.6.x kernel. The stack modifications are described in detail. Also discussed is what hardware and software features are required to achieve page-flipping.
The issues involving page-flipping are described in detail. Also discussed are problems related to this technology concerning the Virtual Memory Manager (VMM) and processor cache. Another issue that is discussed is what would be needed in an API or code changes to enable user-space applications.
The consequences and possible benefits of this technology are called out within the conclusions of this study. Also described are the possible next steps needed to make this technology viable for general use. As faster networks like 10 Gigabit Ethernet become more common-place for servers and desktops, understanding and developing zero-copy receive mechanisms within the Linux kernel and networking stack is becoming more critical.