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What is meant by scheduler activation?
Scheduler activations are a threading mechanism that, when implemented in an operating system’s process scheduler, provide kernel-level thread functionality with user-level thread flexibility and performance.
How do scheduler activations work?
When scheduler activations are used, the kernel assigns a certain number of virtual processors to each process and lets the (user-space) run-time system allocate threads to processors. This mechanism can also be used on a multiprocessor where the virtual processors may be real CPUs.
What are the benefits that Scheduler activations provide?
Scheduler Activations: Effective Kernel Support for the User-Level Management of Parallelism. Advantages of kernel-threads: Order of magnitude better performance than using traditional processes. Each thread gets mapped to a physical processor while it is running.
What is Upcall in scheduler activation?
One event that triggers an upcall occurs when an application thread is about to block. In this scenario, the kernel makes an upcall to the application informing it that a thread is about to block and identifying the specific thread. Then the kernel allocates a new virtual processor to the application.
What is OS LWP?
In computer operating systems, a light-weight process (LWP) is a means of achieving multitasking. In those contexts, the term “light-weight process” typically refers to kernel threads and the term “threads” can refer to user threads.
Which is called as light weight process?
What is the purpose of a scheduler activation?
Scheduler activations are a threading mechanism that, when implemented in an operating system’s process scheduler, provide kernel-level thread functionality with user-level thread flexibility and performance.
How does a scheduler work in a kernel?
It works as likes: The kernel provides an application with a set of virtual processors (LWPs), and the application can schedule user threads onto an available virtual processor. Moreover, the kernel must inform an application about certain events.
Scheduler activations were proposed by Anderson, Bershad, Lazowska, and Levy in Scheduler Activations: Effective Kernel Support for the User-Level Management of Parallelism in 1991. Support was implemented in the NetBSD kernel by Nathan Williams but has since been abandoned in favor of 1:1 threading.
How are virtual processors used in a scheduler?
This mechanism uses a so-called “N:M” strategy that maps some N number of application threads onto some M number of kernel entities, or “virtual processors.” This is a compromise between kernel-level (“1:1”) and user-level (“N:1”) threading.