I understand that Spinlocks are real waste in Linux Kernel Design.
I would like to know why is it like spin locks are good choices in Linux Kernel Design instead of something more common in userland code, such as semaphore or mutex?
Linux – Why are spin locks good choices in Linux Kernel Design instead of something more common in userland code, such as semaphore or mutex
linuxsemaphorespinlock
Best Answer
The choice between a spinlock and another construct which causes the caller to block and relinquish control of a cpu is to a large extent governed by the time it takes to perform a context switch (save registers/state in the locking thread and restore registers/state in another thread). The time it takes and also the cache cost of doing this can be significant.
If a spinlock is being used to protect access to hardware registers or similar where any other thread that is accessing is only going to take a matter of milliseconds or less before it releases the lock then it is a much better use of cpu time to spin waiting rather than to context switch and carry on.