Reverie: Low Pass Filter-Based Switch Buffer Sharing for Datacenters with RDMA and TCP Traffic

The switch buffers in datacenters today are shared by traffic classes with different loss tolerance and reaction to congestion signals. In particular, while legacy applications use loss-tolerant transport, e.g., DCTCP, newer applications require lossless datacenter transport, e.g., RDMA over Converged Ethernet. The allocation of buffers for this diverse traffic mix is managed by a buffer-sharing scheme. Unfortunately, as we analytically show in this paper, the buffer-sharing practices of today's datacenters pose a fundamental limitation to effectively isolate RDMA and TCP while also maximizing burst absorption. We identify two root causes: (i) the buffer-sharing for RDMA and TCP relies on two independent and often conflicting views of the buffer, namely ingress and egress; and (ii) the buffer-sharing scheme micromanages the buffer and overreacts to the changes in its occupancy during transient congestion.

In this paper, we present Reverie, a buffer-sharing scheme, which, unlike prior works, is suitable for both lossless and loss-tolerant traffic classes, providing isolation as well as superior burst absorption. At the core of Reverie lies a unified (consolidated ingress and egress) admission control that jointly optimizes the buffers for both traffic classes. Reverie, allocates buffer based on a low-pass filter that naturally absorbs bursty queue lengths during transient congestion within the buffer limits. Our evaluation shows that Reverie can improve the performance of RDMA as well as TCP in terms of flow completion times by up to 33%.