Giant lock
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It has been suggested that this article or section be merged into Software lockout. (Discuss) Proposed since September 2010. |
In operating systems, a giant lock, also known as a big-lock or kernel-lock, is a lock which may be used in the kernel to provide the concurrency control required by symmetric multiprocessing (SMP) systems.
A giant lock is a solitary global lock that is held whenever a thread enters kernel space, and is released when the thread returns to user space (a system call is the archetypal example). In this model, threads in user space can run concurrently on any available processors or processor cores, but no more than one thread can run in kernel space; any other threads that try to enter kernel space are forced to wait. In other words, the giant lock eliminates all concurrency in kernel space.
By isolating the kernel from concurrency, many parts of the kernel no longer need to be modified to support SMP. By the same token, performance is predictably inefficient on SMP systems. Accordingly, the giant lock approach is commonly seen as a preliminary means of bringing SMP support to an operating system, yielding benefits only in user space. Most modern operating systems use a fine-grained locking approach.
The Linux kernel had a big kernel lock until it was finally replaced by more fine-grained locking mechanisms by Arnd Bergmann in 2011.[1]
