Work-conserving scheduler
In computing and communication systems, a work-conserving scheduler is a scheduler that always tries to keep the scheduled resource(s) busy, if there are submitted jobs ready to be scheduled. In contrast, a work non-conserving scheduler is a scheduler that, in some cases, may leave the scheduled resource(s) idle despite the presence of jobs ready to be scheduled.
For example, when dealing with networking and packet scheduling, a work-conserving scheduler[1][2] leaves the channel idle only when there are no packets to transmit, whereas a non-work conserving one might leave the channel idle also with packets pending to be transmitted.
On the other hand, when referring to CPU scheduling, i.e., threads or processes scheduled over one or more available processors or cores, a work-conserving scheduler[3] ensures that processors/cores are not idle if there are processes/threads ready for execution.
Non-work conserving schedulers are sometimes useful to enhance predictability and reduce termination jitter for the activities carried out by a computing and communication system, and in multi-processor systems they're useful to enhance performance in some scenarios.[4] [5]
References
- ^ [1]Padma Mundur, Improving QOS in IP Networks (course material for Multimedia Networking)
- ^ [2]Jon Crowcroft, Scheduling and queue management (course material for Digital Communications II)
- ^ [3]G. Buttazzo, G. Lipari, L. Abeni, M. Caccamo, Soft Real-Time Systems: Predictability vs. Efficiency, Springer 2005
- ^ [4] A. Fedorova, M. Seltzer and M.D. Smith, "A non-work-conserving operating system scheduler for SMT processors," in Proc. USENIX 2005 Annual Technical Conference, Anaheim, California, April 2005
- ^ [5]J. C. Sáez, J. I. Gomez and M. Prieto, "Improving Priority Enforcement via Non-Work-Conserving Scheduling," Parallel Processing, 2008. ICPP '08. 37th International Conference on, Portland, OR, 2008, pp. 99-106.