Priority-based scheduling policies are commonly used to guarantee that requests submitted to the different service classes offered by cloud providers achieve the desired Quality of Service (QoS). However, the QoS delivered during resource contention periods may be unfair on certain requests. In particular, lower priority requests may have their resources preempted to accommodate resources associated with higher priority ones, even if the actual QoS delivered to the latter is above the desired level, while the former is underserved. Also, competing requests with the same priority may experience quite different QoS, since some of them may have their resources preempted, while others do not. In this paper we present a new scheduling policy that is driven by the QoS promised to individual requests. Benefits of using the QoS-driven policy are twofold: it maintains the QoS of each request as high as possible, considering their QoS targets and available resources; and it minimizes the variance of the QoS delivered to requests of the same class, promoting fairness. We used simulation experiments fed with traces from a production system to compare the QoS-driven policy with a state-of-the-practice priority-based one. In general, the QoS-driven policy delivers a better service than the priority-based one. Moreover, the equity of the QoS delivered to requests of the same class is much higher when the QoS-driven policy is used, particularly when not all requests get the promised QoS, which is the most important scenario. Finally, based on the current practice of large public cloud providers, our results show that penalties incurred by the priority-based scheduler in the scenarios studied can be, on average, as much as 193% higher than those incurred by the QoS-driven one.

中文翻译：

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云中由QoS驱动的调度

基于优先级的调度策略通常用于确保云提供商提供的提交给不同服务类别的请求达到所需的服务质量（QoS）。但是，在资源争用期间传递的QoS对于某些请求可能是不公平的。特别是，即使传递给后者的实际QoS高于所需级别，而前者的服务却不足，但低优先级的请求可能会抢占其资源以容纳与高优先级的资源相关联的资源。同样，具有相同优先级的竞争请求可能会经历完全不同的QoS，因为其中一些请求可能会抢占资源，而其他请求则不会。在本文中，我们提出了一种新的调度策略，该策略由承诺给各个请求的QoS驱动。使用QoS驱动的策略有两个好处：考虑到每个请求的QoS目标和可用资源，它会保持每个请求的QoS尽可能高。并最大程度地减少了传递给相同类别请求的QoS差异，从而提高了公平性。我们使用了来自生产系统的模拟实验，将QoS驱动的策略与基于优先级的实践策略进行了比较。通常，QoS驱动的策略提供比基于优先级的策略更好的服务。此外，当使用QoS驱动的策略时，尤其是在并非所有请求都获得承诺的QoS的情况下，传递给同一类请求的QoS的公平性要高得多，这是最重要的方案。最后，根据大型公共云提供商的当前做法，我们的结果表明，在研究的场景中，基于优先级的调度程序可能会受到惩罚，