#NETMAP ENABLE ZERO COPY WITH HOST STACK DRIVERS#
#NETMAP ENABLE ZERO COPY WITH HOST STACK DRIVER#

When you have the Rx packets on the ring, Netmap updates the count of new frames on the ring and wakes up threads that are sleeping to process the frames.

Simple synchronization-The synchronization mechanism in Netmap is extremely simple. Preventing a copy operation saves a lot of time in an I/O model, and Netmap’s zero-copy model is very effective at increasing performance compared to a traditional Linux I/O model. Hence there is no copy involved in getting the information to the user space. Zero copy-Netmap maps all memory from rings (pool of memory buffers) in a way that makes them directly accessible in the data plane (user space). Since the CSR data plane runs in the user space, when it wants an I/O architecture to deliver receive (Rx) frames from the NIC to the user space (data plane) and transmit (Tx) frames from the data plane to the NIC, it leverages Netmap’s thin I/O stack. Thin I/O stack-Netmap bypasses the Linux networking stack to reduce overhead. Netmap achieves this through the four building blocks of its I/O architecture: Netmap is designed to strip down software layers and get the frame from the wire to the data plane process in user space as quickly as possible. It is important to understand the I/O model before drilling down to packet flow. This section provides an overview of the Netmap I/O model and compares it with a Linux I/O model. Understanding the Netmap I/O model will help you better understand packet flow to and from a CSR VM. Netmap is an open-source I/O infrastructure package that enables the CSR VM to get rid of the multiple software layers in the traditional Linux networking stack I/O model.

#NETMAP ENABLE ZERO COPY WITH HOST STACK DRIVERS#

The CSR VM supports para-virtualized drivers only. However, the performance of emulated drivers is much lower than that of para-virtualized drivers. Therefore, support for emulated drivers is required. Recall from Chapter 1, “Introduction to Cloud,” that in full virtualization, guest operating systems do not require any support from the hypervisor kernel and run as though on real hardware. Hypervisors support emulated drivers because they are required for full virtualization. Para-virtualized drivers are native to hypervisors and perform much better than emulated drivers such as the e1000.

#NETMAP ENABLE ZERO COPY WITH HOST STACK DRIVER#

This driver can either be a para-virtualized driver (for example, VMXNET3) or a real/emulated driver (for example, e1000). From Figure 4-5, you can see that the hypervisor presents a virtual NIC to its guest VM by using a driver.

Netmap enable zero copy with host stack