Resource sharing under global scheduling with partial processor bandwidth

Multiprocessor Real-Time Locking Protocols: A Systematic Review

“…Specifically, Hohmuth and Härtig proposed a mechanism that they termed helping:whenever a blocked client (i.e., a client thread that seeks to rendezvous with a server thread that is not waiting to accept a synchronous IPC message) is selected by the scheduler, the server process is dispatched instead [103] (see also time-slice donation [185]). 6 Hohmuth and Peter extended Hohmuth and Härtig's helping approach to multiprocessors (under P-FP scheduling) and systematically considered key design choices and challenges. Specifically, with local helping, 7 a preempted resource server is migrated (i.e., pulled) to the core of the blocked client, at which point the uniprocessor helping mechanism [103] can be applied-an instance of the allocation inheritance principle (Section 3.5).…”

“…The sleep and callback approach is equivalent to self-suspending clients, which comes with the typical advantage that blocked clients yield the processor to lower-priority tasks, but which also introduces the typical analytical challenges and overhead issues. Since Hohmuth and Peter expected critical sections (i.e., server request handlers) in their system to be quite short, and due 6 Hohmuth and Härtig's helping mechanism [103] is named in analogy to the "helping" employed in wait-free algorithms [102], but fundamentally a different mechanism. "Helping" in wait-free algorithms does not rely on any support by the OS [102]; rather, it is realized exclusively with a processor's atomic operations (such as an atomic compare-and-swap instruction).…”

“…Finally, several authors have considered synchronization needs in hierarchical multiprocessor real-time systems (i.e., systems in which there is a hierarchy of schedulers) [6,7,9,31,120,152,153]. In such systems, tasks are typically encapsulated in processor reservations, resource servers, or, in the case of virtualization, virtual machines, and thus prone to preemptions in the middle of critical sections.…”