Datacenter congestion control: identifying what is essential and making it practical
Datacenter congestion control: identifying what is essential and making it practical
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DOI：
10.1145/3371927.3371932
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发表时间：
2019-11
期刊：
影响因子：
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通讯作者：
Aisha Mushtaq;R. Mittal;J. McCauley;Mohammad Alizadeh;Sylvia Ratnasamy;S. Shenker
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文献类型：
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作者：
Aisha Mushtaq;R. Mittal;J. McCauley;Mohammad Alizadeh;Sylvia Ratnasamy;S. Shenker
近年来出现了大量关于数据中心拥塞控制机制的论文。在这篇社论中，我们提出了一个问题，即拥塞控制涉及主机响应来自网络的简单拥塞信号，并且性能目标是减少流完成时间的平均度量，对于这种常见情况，是否需要进行大量的研究。我们提出这个问题是因为我们发现，在拥塞控制算法的所有可能变化中，最重要的特征是交换机调度算法。更具体地说，我们发现只要主机上的速率设置算法合理，使用最短剩余处理时间（SRPT）的拥塞控制机制就能获得更好的性能。我们进一步发现，虽然SRPT的性能对主机行为相当稳健，但使用FIFO或公平排队等调度算法的方案的性能更关键地取决于速率设置算法，并且它们的性能通常比SRPT所能达到的性能更差。鉴于这些发现，我们接着会问，在不需要定制硬件的情况下在交换机中实现SRPT是否可行。我们观察到存在近似的和可部署的SRPT （ADS）设计，它利用了几乎所有商品交换机中支持的少量优先级队列，并且只需要在主机和交换机中进行软件更改。我们对一个非常简单的ADS设计的评估表明，它可以实现接近真正的SRPT的性能，并且明显优于FIFO。因此，对于我们的基本问题——最近对数据中心拥塞控制算法的大量研究是否需要用于常见情况——的答案是否定的。
Recent years have seen a slew of papers on datacenter congestion control mechanisms. In this editorial, we ask whether the bulk of this research is needed for the common case where congestion control involves hosts responding to simple congestion signals from the network and the performance goal is reducing some average measure of flow completion time. We raise this question because we find that, out of all the possible variations one could make in congestion control algorithms, the most essential feature is the switch scheduling algorithm. More specifically, we find that congestion control mechanisms that use Shortest-Remaining-Processing-Time (SRPT) achieve superior performance as long as the rate-setting algorithm at the host is reasonable. We further find that while SRPT's performance is quite robust to host behaviors, the performance of schemes that use scheduling algorithms like FIFO or Fair Queuing depend far more crucially on the rate-setting algorithm, and their performance is typically worse than what can be achieved with SRPT. Given these findings, we then ask whether it is practical to realize SRPT in switches without requiring custom hardware. We observe that approximate and deployable SRPT (ADS) designs exist, which leverage the small number of priority queues supported in almost all commodity switches, and require only software changes in the host and the switches. Our evaluations with one very simple ADS design shows that it can achieve performance close to true SRPT and is significantly better than FIFO. Thus, the answer to our basic question - whether the bulk of recent research on datacenter congestion control algorithms is needed for the common case - is no.