1，SR-IOV （single root io virtualization）
SR-IOV is a specification that allows a pcie device to appear to be multiple separate PCIe devices. SR-IOV works by introducing the idea of physical functions(PFs) and virtual functions(VFs).Physical functions (PFs) are full-featured PCIe functions; virtual functions (VFs) are “lightweight” functions that lack configuration resources. (I’ll explain why VFs lack these configuration resources shortly.)
The PCI SIG SR-IOV specification indicates that each device can have up to 256 VFs. Depending on the SR-IOV device in question and how it is made, it might present itself in a variety of ways.These are, of course, theoretical maximums. Because each VF requires actual hardware resources, practical limits are much lower. Currently, 64 VFs seems to be the upper limit for most devices.
2，DMA
Direct memory access (DMA) is a method that allows an input/output (I/O) device to send or receive data directly to or from the main memory, bypassing the CPU to speed up memory operations.
The process is managed by a chip known as a DMA controller (DMAC).
A computer's system resource tools are used for communication between hardware and software. The four types of system resources are:
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I/O addresses.
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Memory addresses.
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Interrupt request numbers (IRQ).
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Direct memory access (DMA) channels
DMA channels are used to communicate data between the peripheral device and the system memory. All four system resources rely on certain lines on a bus. Some lines on the bus are used for IRQs, some for addresses (the I/O addresses and the memory address) and some for DMA channels.
A DMA channel enables a device to transfer data without exposing the CPU to a work overload. Without the DMA channels, the CPU copies every piece of data using a peripheral bus from the I/O device. Using a peripheral bus occupies the CPU during the read/write process and does not allow other work to be performed until the operation is completed.
3，IOMMU
IOMMU全称是Input/Output Memory Management Unit，翻译是输入输出的内存管理单元。Intel芯片上叫 VT-d （Virtualization Technology for Directed I/O ），AMD还是叫做IOMMU。
IOMMU（Input/Output Memory Management Unit）是内存管理单位（Memory Management Unit），它的功能是连接DMA-capable I/O总线（Direct Memory Access-capable I/O Bus）和主存（main memory）。传统的内存管理单位将使用CPU访问虚拟地址转换为实际物理地址。传统的内存管理单位将使用CPU访问的虚拟地址转换为实际物理地址。IOMMU则是把设备（device）虚拟地址转换为物理地址。
图二：