Size-based task assignment with cycle stealing under central queue (SBCS-CQ):

The SBCS-CQ policy (see Figure 5.1(b)) is defined for the central queue model. Whenever the short job host becomes idle, it picks the first short job in the queue to run. Whenever the long job host becomes idle, it picks the first long job in the queue. However, if there is no long job, the long host picks the first short job in the queue. In SBCS-CQ, we introduce a minor technique that can slightly improve mean response time. Whereas in SBCS-ID the short and long hosts are designated in advance, in SBCS-CQ we allow renaming of hosts; i.e. if the long host is working on a short job, and the short host is idle, then the long host is renamed the short host and vice versa. Thus in SBCS-ID, there could be one short in front of one long job in the system with an idle (short) server, while this could not happen under SBCS-CQ.

Figure 5.1: Size-based task assignment with cycle stealing.

(a) SBCS-ID

(b) SBCS-CQ