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What is the justification for having spin locks in Linux kernel?
Reason: Support your driver take a spinlock that control access to the device and then issues an interrupt. This causes the interrupt handler to run. Now the interrupt handler also needs the lock to access the device. If the interrupt handler runs on the same processor, it will start spinning.
How are locks implemented by kernel?
Two Main Types of Kernel Locks: Spinlocks and Mutexes There are two main types of kernel locks. The second type is a mutex ( include/linux/mutex. h ): it is like a spinlock, but you may block holding a mutex. If you can’t lock a mutex, your task will suspend itself, and be woken up when the mutex is released.
In which context is it a good idea for a thread to sleep while holding a spinlock?
The idea is to use a spinlock when trying to access a resource locked by a currently-running thread, but to sleep if the thread is not currently running. (The latter is always the case on single-processor systems.)
Why do Spinlocks disable interrupts?
To avoid priority inversion on same core. In case of multiprocessor system also process disables interrupt on its own core to ensure it gets the enough cpu time to run.
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 spin lock in Linux?
The basic form of locking in the Linux kernel is the spinlock. Spinlocks take their name from the fact that they continuously loop, or spin, waiting to acquire a lock. This section of code sets the spin_lock to “unlocked,” or 0, on line 66 and initializes the other variables in the structure.
What is meant by big kernel lock?
In operating systems, a giant lock, also known as a big-lock or kernel-lock, is a lock that may be used in the kernel to provide concurrency control required by symmetric multiprocessing (SMP) systems. In other words, the giant lock eliminates all concurrency in kernel space.
Can we use spinlock in interrupt handler?
The answer is yes and no. you can use the up and unlock, but you can’t use down and lock, as these are blocking calls which put the process to sleep and we are not supposed to sleep in interrupt handlers.
How do I stop busy waiting?
To avoid busy waiting, a semaphore may use an associated queue of processes that are waiting on the semaphore, allowing the semaphore to block the process and then wake it when the semaphore is incremented.
Why is ” sleeping ” not allowed while holding a spin lock?
You cannot hold a spin lock while you acquire a semaphore, because you might have to sleep while waiting for the semaphore, and you cannot sleep while holding a spin lock (from “Linux Kernel Development” by Robert Love).
When to release a lock on a spinlock?
When the time slice for thread B will finish and sleep time for thread would have ended, thread A would execute using its time slice and once done will release the lock. Is it not the case? – Sumit TrehanSep 20 ’14 at 17:01 2 @SumitTrehan: Good point.
Why is preemption disabled when holding a spinlock?
However, in linux, preemption is always disabled when a spinlock is held (or about to be held). This is because if a thread is holding a spinlock while not running, other threads waste lots of time spinning on the lock, and there is potential for deadlock with interrupt handlers.