Network Interface Architecture for Remote Indirect Memory Access (RIMA) in Datacenters

Abstract

Remote Direct Memory Access (RDMA) fabrics such as InfiniBand and Converged Ethernet report latency shorter by a factor of 50 than TCP. As such, RDMA is a potential replacement for TCP in datacenters (DCs) running low-latency applications, such as Web search and memcached. InfiniBand’s Shared Receive Queues (SRQs), which use two-sided send/recv verbs (i.e., channel semantics ), reduce the amount of pre-allocated, pinned memory (despite optimizations such as InfiniBand’s on-demand paging (ODP)) for message buffers. However, SRQs are limited fundamentally to a single message size per queue, which incurs either memory wastage or significant programmer burden for typical DC traffic of an arbitrary number (level of burstiness) of messages of arbitrary size. We propose remote indirect memory access (RIMA) , which avoids these pitfalls by providing (1) network interface card (NIC) microarchitecture support for novel queue semantics and (2) a new “verb” called append . To append a sender’s message to a shared queue, the receiver NIC atomically increments the queue’s tail pointer by the incoming message’s size and places the message in the newly created space. As in traditional RDMA, the NIC is responsible for pointer lookup, address translation, and enforcing virtual memory protections. This indirection of specifying a queue (and not its tail pointer, which remains hidden from senders) handles the typical DC traffic of an arbitrary sender sending an arbitrary number of messages of arbitrary size. Because RIMA’s simple hardware adds only 1--2 ns to the multi-\mu s message latency, RIMA achieves the same message latency and throughput as InfiniBand SRQ with unlimited buffering. Running memcached traffic on a 30-node InfiniBand cluster, we show that at similar, low programmer effort, RIMA achieves significantly smaller memory footprint than SRQ. However, while SRQ can be crafted to minimize memory footprint by expending significant programming effort, RIMA provides those benefits with little programmer effort. For memcached traffic, a high-performance key-value cache ( FastKV ) using RIMA achieves either 3× lower 96 th-percentile latency or significantly better throughput or memory footprint than FastKV using RDMA.