Contents
What is saved during context switching?
In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point. This allows multiple processes to share a single central processing unit (CPU), and is an essential feature of a multitasking operating system.
What is the overall effect of a context switch?
Context switching is particularly destructive because it takes a lot of time and effort to pick up where you left off and get back in the zone. All this loss of time, energy, and mental resources have far-reaching effects — causing mental fatigue and, from a bigger picture, keeping us from reaching our goals.
Is context switching interrupt?
A context switch looks just like an interrupt. The state is stored in the stack as per usual. However, the location of that stack and any extra state information is stored elsewhere (in the thread). A new set of data from another thread is then substituted with the current data and the ISR returns.
Which is faster context switching or memory copying?
In other words, a context switch is a bit quicker than copying 64 KiB of memory from one location to another. 1-2 us is not a long time by any measure, except when you’re really trying to optimize for extremely low latencies or high loads.
Why does context switching take so long in Linux?
A condition variable used by two threads to signal an event to each other. There are additional factors context switching time depends on; for example, on a multi-core CPU, the kernel can occasionally migrate a thread between cores because the core a thread has been previously using is occupied.
What happens to memory when switching between programs?
And when switching between programs, the operating system would swap out the running program’s memory, swap in a new program and start it running again. Of course, this is extremely slow. There has to be a better solution, and one that also protects the OS memory from user-mode programs.
Why do I not use context switching in benchmarks?
Frequent switches back and forth between the two threads will cause a lot of such thrashing. In my benchmarks I am not measuring this indirect cost, because it’s pretty difficult to avoid in any form of multi-tasking.