SMP

The full name of SMP is "Symmetrical Multi-Processing" technology, which refers to a set of processors (multiple CPUs) on a single computer, sharing memory subsystems and bus structures among CPUs. It is a relatively widely used parallel technology in terms of asymmetric multiprocessing technology. In this architecture, a computer no longer consists of a single CPU, while multiple processors simultaneously run a single copy of the operating system and share memory and other resources of a computer. Although using multiple CPUs at the same time, from a management point of view, they behave like a stand-alone machine. The system distributes task queues symmetrically across multiple CPUs, which greatly improves the overall system's data processing capabilities. All processors have equal access to memory, I/O, and external interrupts. In a symmetric multiprocessing system, system resources are shared by all CPUs in the system and the workload can be evenly distributed over all available processors.

The dual-CPU system we usually refer to is actually the most common type of symmetric multi-processing system. It is often referred to as “2-way symmetric multi-processing”. It has not much practical use in common commercial and domestic applications. , But in professional production, such as 3DMax Studio, Photoshop and other software applications have obtained very good performance, is a good partner for the formation of cheap workstations. With the improvement of the level of user applications, it is difficult to use only a single processor to meet the needs of practical applications. Therefore, server manufacturers have adopted a symmetric multi-processing system to solve this problem. In the domestic market, these types of models generally have 4 or 8 processors, and a few have 16 processors. However, in general, the SMP structure has poor machine scalability, and it is difficult to achieve more than 100 multiprocessors. The conventional one is generally 8 to 16, but this is sufficient for most users. The advantage of this kind of machine is that it is not different from the computer or workstation. The change of programming is relatively small. It is relatively easy to change the program written by the computer workstation if it is to be used on the SMP machine. . The SMP structure has poor model availability. Because 4 or 8 processors share an operating system and a memory, once the operating system has a problem, the entire machine is completely lost. And because of the poor scalability of this machine, it is not easy to protect users' investment. However, this type of technology is relatively mature, and the corresponding software is also relatively large, so now a large number of parallel machines are introduced on the domestic market. The most common symmetric multiprocessing systems in PC servers typically use 2, 4, 6, or 8 processors. At present, UNIX servers can support systems with up to 64 CPUs. For example, the key technology of Sun Enterprise's Enterprise 10000.SMP system is how to better solve the mutual communication and coordination problems of multiple processors.

To establish an SMP system, the most critical point is to need a suitable CPU. The CPUs that we usually see are all single-use, so we can't see any difference between them. However, in fact, supporting SMP is not unconditional. You can build a multi-processing system by using a few CPUs at will. Tianfang night talks. To implement SMP functionality, the CPU we use must have the following requirements:
1. The CPU must have built-in APIC (Advanced Programmable Interrupt Controllers) units. The core of the Intel multiprocessing specification is the use of Advanced Programmable Interrupt Controllers (APICs). The CPU completes the communication between them by sending interrupts to each other. By attaching actions to interrupts, different CPUs can control each other to some degree. Each CPU has its own APIC (which becomes the local APIC for that CPU), and there is also an I/O APIC to handle interrupts caused by I/O devices. This I/O APIC is installed on the motherboard, but each The APIC on the CPU is indispensable, otherwise it will not be able to handle interrupt coordination between multiple CPUs.

2, the same product model, the same type of CPU core. For example, although Athlon and Pentium III each have built-in APIC units, it is not possible to have them build SMP systems together. Of course, even for Celeron and Pentium III, the odds are zero, even for the Coppermine core Pentium III. And the Tualatin's Pentium III can't build SMP systems either - because their execution instructions are not exactly the same, APIC's interrupt coordination is also very different.

3, the exact same operating frequency. If you want to build a dual Pentium III system, you must have two 866MHz or two 1000MHz processors. You cannot use one 866MHz and the other 1000MHz to set up, otherwise the system will not be able to light up properly.

4. Keep the same product serial number as possible. Even the same core processor with the same frequency can cause unpredictable problems due to different production batches. When two production batches of CPUs are running as dual processors, it is possible that one CPU will be overburdened, and the other will not be able to achieve maximum performance, and worse, may cause crashes. , Should choose the same batch of processors as possible to set up SMP system.