Online services play a major role in our everyday life for communication, entertainment, socializing, e-commerce, etc. These services run inside the datacenter under strict tail-latency service level objectives in order to remain interactive. The emergence of new hardware for IO has enabled microsecond-scale datacenter communications that challenge the efficiency of existing operating system and network mechanisms. Also, new in-network programmable devices start being deployed in datacenters and introduce a new computing paradigm that shifts functionality traditionally performed at the end-points to the network. In this talk I will revisit the operating systems, networking, and distributed systems infrastructure specifically targeting latency-critical datacenter systems, while drawing intuition from basic queueing theory results. In the first part of the talk, I will focus on ZygOS[SOSP 2017], a system optimized for μs-scale, in-memory computing on multicore servers. ZygOS implements a work-conserving scheduler within a specialized operating system designed for high request rates and a large number of network connections. ZygOS revealed the challenges associated with serving remote procedure calls (RPCs) on top of a byte-stream oriented protocol, such as TCP. In the second part of the talk, I will present R2P2[ATC 2019]. R2P2 is a transport protocol specifically designed for datacenter RPCs, that exposes the RPC abstraction to the endpoints and the network, making RPCs first-class datacenter citizens. R2P2 enables pushing functionality, such as scheduling, fault-tolerance, and tail-tolerance, inside the transport protocol. I will show how using R2P2 allowed us to offload RPC scheduling to programmable switches that can schedule requests directly on individual CPU cores.