# 2.6.4 带宽控制

系统引入任务组的基本目的之一，就是实现资源的分配与控制，对CPU时间的限制通过带宽控制来实现，本节我们就来一探究竟。实时任务和普通任务都有带宽控制的逻辑，我们这里只讨论CFS的带宽控制。

带宽控制的总体思路如下：系统为任务组设置带宽额度，任务组中的各个cfs\_rq首先需要向任务组（task\_group）申请时间，如果申请成功，则cfs\_rq中的任务可以被CFS调度运行，如果申请失败（例如当前周期内任务组的时间配额已经用完），则调度器会将cfs\_rq挂起（throttle）；系统通过定时器周期性地为任务组重新分配时间额度，并将挂起的cfs\_rq解挂（unthrottle）。

下面我们深入代码，从各个方面详细分析带宽控制的实现方式。


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