What is smp?

SMP, or Symmetric Multiprocessing, is a multiprocessing architecture where multiple processors share a single shared memory space. This means that all processors have access to the same physical memory and can execute instructions concurrently. SMP systems are often used in servers and workstations where high performance is required.

Here's some key information about SMP:

  • Shared Memory: The defining characteristic of SMP is the shared memory architecture. This allows processors to communicate with each other by reading and writing to the same memory locations.

  • Symmetric Access: "Symmetric" refers to the fact that all processors have equal access to memory, I/O, and other resources. There's no master processor assigning tasks or managing resources. This distributed responsibility design enables better scalability.

  • Operating System Support: SMP systems require an operating system designed to support multiprocessing. The OS is responsible for scheduling tasks across multiple processors, managing memory access, and ensuring data consistency. Modern operating systems such as Linux, Windows, and macOS all support SMP.

  • Cache Coherency: Maintaining cache coherency is a crucial challenge in SMP systems. Since each processor has its own cache, the system must ensure that all caches contain consistent data. Various protocols (e.g., MESI) are used to achieve this.

  • Scalability: SMP systems can scale to a certain extent by adding more processors. However, there are limits to scalability due to factors such as memory bandwidth limitations and cache coherency overhead. Adding more cores is not a guaranteed approach to greater performance.

  • Advantages:

    • Improved performance compared to single-processor systems
    • Simplified programming model compared to other multiprocessing architectures (like distributed memory systems)
  • Disadvantages:

    • Limited scalability compared to distributed memory systems
    • Cache coherency overhead can reduce performance
    • More complex hardware and software design compared to single-processor systems