Multitasking in Embedded Linux

Multitasking in Embedded Linux

In the computer field, "task" has the sense of a real-time application, as distinguished from process, which takes up space (memory), and execution time.

 A process, or task, can be seen as a set of allocated resources

Process switching makes big memory consumption. Because, when we created a new process, we need to create a process descriptor and allocate another memory region as its work space.

However, Thread allows you use the same memory in a process to work on, so you don't need to create an extra memory. So real-time linux use just one main process which includes threads to realize multitasking in embedded linux.

But there's more. Threads also happen to be extremely nimble. Compared to a standard fork(), they carry a lot less overhead. The kernel does not need to make a new independent copy of the process memory space, file descriptors, etc. That saves a lot of CPU time, making thread creation ten to a hundred times faster than new process creation. Because of this, you can use a whole bunch of threads and not worry too much about the CPU and memory overhead incurred. You don't have a big CPU hit the way you do with fork(). This means you can generally create threads whenever it makes sense in your program.

Threads differ from traditional multitasking operating system processes in that:

• processes are typically mean time, while threads exist as subsets of a process
• processes carry considerably more state information than threads, whereas multiple threads within a process share process state as well as memory and other resources.
• processes have separate address spaces, whereas threads share their address space.
• processes interact only through system-provided inter-process communication mechanisms.
• Context switching between threads in the same process is typically faster than context switching between processes.