On achieving low latency in data centers

Today's data centers face extreme challenges in providing low latency for online services such as web search, social networking, and recommendation systems. Achieving low latency is important as it impacts user experience, which in turn impacts operator revenue. However, most current congestion control protocols approximate Processor Sharing (PS), which is known to be sub-optimal for minimizing latency. In this paper, we propose Router Assisted Capacity Sharing (RACS), a data center transport protocol that minimizes flow completion times by approximating the Shortest Remaining Processing Time (SRPT) scheduling policy, which is known to be optimal, in a distributed manner. With RACS, flows are assigned weights which determine their relative priority and thus the rate assigned to them. By changing these weights, RACS can approximate a range of scheduling disciplines. Through extensive ns-2 simulations, we demonstrate that RACS outperforms TCP, DCTCP, and RCP in data center environments. In particular, it improves completion times by up to 95% over TCP, 88% over DCTCP, and 80% over RCP. Our results also show that RACS can outperform deadline-aware transport protocols for typical data center workloads.