Understanding the Distinctions Between Multiprocessing and Multithreading
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Chapter 1: Introduction to Embedded Systems
Embedded systems are essential components in modern computing, particularly when discussing multiprocessing and multithreading. Understanding these concepts is crucial for effective system design.
Section 1.1: Defining Processes and Threads
A process can be defined as a series of instructions that are loaded into memory and executed by the processor. This execution state, where the process is actively running, characterizes it as a process. Conversely, a thread also consists of a set of instructions loaded into memory for execution. However, a process typically contains one or more threads, with threads functioning as the individual units of execution within the process.
Section 1.2: Understanding Multiprocessing
When discussing processes, it is essential to recognize that each process operates within its own memory space, which includes both physical and virtual address spaces. Each process utilizes its own set of instructions and data segments that are mapped to unique physical and virtual addresses. This is achieved through a single Translation Table that the Memory Management Unit (MMU) uses to translate these addresses.
In a multiprocessing environment, when switching between processes, the system saves the current CPU and memory state before restoring the state of the next process. This context switching can be resource-intensive, as it often involves flushing the Translation Lookaside Buffers (TLBs) and caches associated with the MMU. ARM has addressed this issue by allowing multiple process Translation Table entries to coexist in the TLBs using an Address Space Identifier (ASID). Therefore, switching processes not only requires saving the CPU's internal register state but also the entire memory and MMU configuration.
Section 1.3: Inter-Process Communication (IPC)
Since each process has a distinct memory view, Inter-Process Communication (IPC) sometimes necessitates hardware support or specific software arrangements from the kernel. This kernel has a comprehensive understanding of each process's physical address mapping, utilizing mechanisms such as mailboxes, pipes, and sockets for effective communication.
Chapter 2: Exploring Multithreading
A single process can comprise multiple threads, where we refer specifically to software threads. Each thread maintains its own CPU state, so switching between threads primarily involves the context switching of the CPU's internal registers. Unlike processes, threads share the same MMU translation table and, consequently, have a unified view of physical memory. This shared memory space simplifies Inter-Thread Communication (ITC), often eliminating the need for special arrangements at the kernel level.
The first video titled "Difference between Multiprocessing and Multithreading" elaborates on the fundamental differences and implications of choosing one approach over the other.
The second video, "Embedded System | Multiprocessing & Multitasking," provides insights into how these concepts are applied within embedded systems, enhancing your understanding of their practical applications.