Spinlock versus Semaphore

Question

What are the basic differences between a semaphore & spin-lock?

When would we use a semaphore over a spin-lock?

Answer 1

I am not a kernel expert but here are few points:

Even uniprocessor machine can use spin-locks if kernel preemption is enabled while compiling the kernel. If kernel preemption is disabled then spin-lock (perhaps) expands to a void statement.

Also, when we are trying to compare Semaphore vs Spin-lock, I believe semaphore refers to the one used in kernel - NOT the one used for IPC (userland).

Basically, spin-lock shall be used if critical section is small (smaller than the overhead of sleep/wake-up) and critical section does not call anything that can sleep! A semaphore shall be used if critical section is bigger and it can sleep.

Raman Chalotra.