Bandwidth transfer is often required and deadline missing occurs when a real-time system changes its running mode.In order to solve this problem,based on the real-time task set scheduled with the earliest deadline first algorithm,the bandwidth transfer caused by new tasks' insertion and current tasks' acceleration is studied.According to the three stages of the old mode,the transition process,and the new mode,a model of multitask bandwidth transfer is presented.Some current tasks are compressed to release bandwidth.Even the system runs at full load,it is proved that deadline missing is only possible before the transition process as long as the sum of the utilizations(bandwidths) of all the tasks in the new mode is not greater than one,and thus the starting and ending points of the transition process are defined.Simulations results show that this model gives an overall description of the bandwidth transfer of multitask.%当一个实时系统的运行模式发生改变时,常需要进行带宽转让,并造成截止期丢失.为此,基于最早截止期优先调度的实时任务集,研究因出现新任务插入、现行任务加速而引起的带宽转让问题,依据老模式、过渡过程和新模式这3个阶段,提出一种多任务带宽转让模型,通过压缩某些现有任务来释放带宽,并证明即使系统在满负荷运行的情况下,只要新模式下所有任务的使用率(带宽)之和不大于l,截止期丢失的现象不可能出现在过渡过程后,并据此定义过渡过程的起点和终点.仿真结果表明,该模型能较为全面地展示多任务的带宽转让过程.
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