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Why would you use a spin lock instead of a mutex?
If a thread cannot lock the mutex, it won’t be put to sleep immediately, since the mutex might get unlocked pretty soon, so instead the mutex will first behave exactly like a spinlock.
Why are spinlocks useful?
Spinlocks are useful for multiprocessor systems where a thread can run in a busy-loop (for a short period of time) rather than incurring the overhead of being put in a sleep queue. Mutexes are useful for locking resources.
Is SpinLock faster than mutex?
Thus, mutexes were, in fact, slower than spinlocks in some benchmarks. However, modern mutex implementations avoid all syscalls if there’s no contention. A state of a spinlock is just a single boolean variable, while for a mutex you also need a queue of waiting threads.
What is main disadvantage of Spinlocks?
The primary disadvantage of a spinlock is that, while waiting to acquire a lock, it wastes time that might be productively spent elsewhere. Do not acquire the lock. In many situations it is possible to design data structures that do not require locking, e.g. by using per-thread or per-CPU data and disabling interrupts.
In which scenarios busy waiting is better than spin lock?
So a spin-lock is implemented using busy-waiting. Busy-waiting is useful in any situation where a very low latency response is more important than wasting CPU cycles (like in some types of embedded programming).
What is Spin_lock_irqsave?
spin_lock_irqsave is basically used to save the interrupt state before taking the spin lock, this is because spin lock disables the interrupt, when the lock is taken in interrupt context, and re-enables it when while unlocking. The interrupt state is saved so that it should reinstate the interrupts again.
What does it mean to take a spinlock in Linux?
With spinlocks, taking the lock means just “spinning” (i.e. doing nothing in a loop) until noone else has the lock. With conditions, if a task attempts to take the lock but is blocked because another task holds it, the newcomer enters a wait queue; the release operation signals to any waiting task that the lock is now available.
Is it safe to use a spinlock on a single CPU?
Using spinlocks on a single-core/single-CPU system makes usually no sense, since as long as the spinlock polling is blocking the only available CPU core, no other thread can run and since no other thread can run, the lock won’t be unlocked either. IOW, a spinlock wastes only CPU time on those systems for no real benefit.
What is the big kernel lock in Linux?
Up through Linux 2.0, the kernel was almost purely a single-tasking program: whenever the CPU was running kernel code, only one CPU core was used, because there was a single spin lock protecting all shared resources, called the Big Kernel Lock (BKL).
What happens when a thread tries to lock a spinlock?
When a thread tries to lock a spinlock and it does not succeed, it will continuously re-try locking it, until it finally succeeds; thus it will not allow another thread to take its place (however, the operating system will forcefully switch to another thread, once the CPU runtime quantum of the current thread has been exceeded, of course).