What is Intel's vt-d technology?

Vt-d Technology:

We know that for servers, an important component of I/O,CPU's computational power is that it can process data faster, but only if the data is able to reach the CPU smoothly, so that the I/O capability is an important part of the enterprise architecture, whether it be storage, network, graphics card, memory, etc. To this end, people not only invest in transmission bandwidth (from Gigabit Ethernet to Gigabit Ethernet to Gigabit Ethernet), but also invest heavily in a variety of systems and architectures (such as higher throughput RAID series, multi-tier data centers)

The key to I/O virtualization is to solve the problem of data exchange between I/O devices and virtual machines, and this is mainly related to DMA direct memory access, and IRQ interrupt requests, as long as the isolation, protection, and performance issues of these two aspects are resolved, which is successful I/O virtualization. Like the Intel Vt-i and Vt-x on the processor, Intel Vt-d technology is a hardware-assisted virtualization technology based on North Bridge, which provides a new way of I/O virtualization by providing DMA virtualization and IRQ virtualization hardware built into the bridges, Intel vt-d can greatly improve the reliability, flexibility and performance of I/O in virtual environments.

The traditional iommus (I/O memory Management units,i/o RAM Management Unit) provides a centralized way to manage all dma--in addition to traditional internal DMA, including AGP Gart, TPT, RDMA over tcp/ IP, such as these special DMA, it is easy to implement by differentiating devices in the memory address range, but it is not easy to achieve DMA isolation, so vt-d realizes the existence of multiple DMA protection zones by updating the designed IOMMU architecture, and finally realizes DMA virtualization. This technique is also called DMA remapping.

I/O devices generate very many interrupt requests, and I/O virtualization must properly detach these requests and route them to different virtual machines. Interrupt requests for legacy devices can be in two ways: one that is routed through the I/O interrupt controller, one that is sent directly through the DMA write request (message signaled interrupts, and messages are interrupted), because the destination memory address needs to be embedded within the DMA request. Therefore, this architecture requires full access to all memory addresses, and does not enable interrupt isolation vt-d implementation of the interrupt remapping (interrupt-remapping) schema by redefining the MSI format to solve this problem, the new MSI is still a DMA write request form, Instead of embedding the destination memory address, it is replaced by a message ID that, by maintaining a table structure, allows the hardware to identify different virtual machine regions with different message IDs. The interrupt remapping implemented by VT-D can support all I/O sources, including Ioapics, as well as all interrupt types, such as the usual MSI and extended msi-x.

There are many changes vt-d, such as hardware buffering, address translation, etc., through these various measures, vt-d realize the North Bridge chip level I/O device virtualization. Vt-d finally embodied in the virtualization model is the new addition of two device virtualization methods:

Direct I/O device allocation, the virtual machine allocates the physical I/O device directly to the virtual machine, and under this model, the driver inside the virtual machine communicates directly with the hardware device, which requires only a small amount, or is not managed by VMM. For system robustness, hardware virtualization is required to isolate and protect hardware resources for only the specified virtual machines, and the hardware also requires multiple I/O container partitions to serve multiple virtual machines at the same time, which almost completely eliminates the need to run drivers in VMM. For example, CPU, although CPU is not a normal I/O device-but it is actually allocated to the virtual machine in this way, of course, CPU resources are still under the management of VMM.

Using vt-d technology, virtual machines are able to use direct I/O device allocation or I/O device sharing in place of traditional device emulation/additional device interfaces, thereby greatly enhancing virtualized I/O performance.

Http://www.cnblogs.com/dkblog/archive/2011/12/12/2285404.html

What is Intel's vt-d technology?