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Performance Interfaces for Network Functions

George Candea, Rishabh Ramesh Iyer

Modern programmers routinely use third-party code, and infrastructure operators deploy software they did not write. This would not be possible without semantic interfaces---documentation, header files, specifications---that succinctly describe what that third-party code does. We propose performance interfaces as a way to describe a system's performance, akin to how a semantic interface describes its functionality. We concretize this idea in the domain of network functions (NFs) and present a tool (PIX) that automatically extracts performance interfaces from NF implementations. We evaluate PIX on 12 NFs, including several used in production. The resulting performance interfaces are accurate yet orders of magnitude simpler than the code itself and take minutes to extract. We show how developers and operators can use performance interfaces to identify performance regressions, diagnose and fix performance bugs and identify the latency impact of NIC offloads.

USENIX Association2022

Performance Contracts for Software Network Functions

George Candea, Luis David Figueiredo Mascarenhas Moreira Pedrosa, Rishabh Ramesh Iyer, Solal Vincenzo Pirelli, Arseniy Zaostrovnykh

Software network functions (NFs), or middleboxes, promise flexibility and easy deployment of network services but face the serious challenge of unexpected performance behaviour. We propose the notion of a performance contract, a construct formulated in terms of performance critical variables, that provides a precise description of NF performance. Performance contracts enable fine-grained prediction and scrutiny of NF performance for arbitrary workloads, without having to run the NF itself. We describe BOLT, a technique and tool for computing such performance contracts for the entire software stack of NFs written in C, including the core NF logic, DPDK packet processing framework, and NIC driver. BOLT takes as input the NF implementation code and outputs the corresponding contract. Under the covers, it combines pre-analysis of a library of stateful NF data structures with automated symbolic execution of the NF’s code. We evaluate BOLT on four NFs—a Maglev-like load balancer, a NAT, an LPM router, and a MAC bridge—and show that its performance contracts predict the dynamic instruction count and memory access count with a maximum gap of 7% between the real execution and the conservatively predicted upper bound. With further engineering, this gap can be reduced.

USENIX ASSOC2019

Verifying Software Network Functions with No Verification Expertise

George Candea, Luis David Figueiredo Mascarenhas Moreira Pedrosa, Rishabh Ramesh Iyer, Solal Vincenzo Pirelli, Matteo Rizzo

We present the design and implementation of Vigor, a software stack and toolchain for building and running software network middleboxes that are guaranteed to be correct, while preserving competitive performance and developer productivity. Developers write the core of the middlebox---the network function (NF)---in C, on top of a standard packet-processing framework, putting persistent state in data structures from Vigor's library; the Vigor toolchain then automatically verifies that the resulting software stack correctly implements a specification, which is written in Python. Vigor has three key features: network function developers need no verification expertise, and the verification process does not require their assistance (push-button verification); the entire software stack is verified, down to the hardware (full-stack verification); and verification can be done in a pay-as-you-go manner, i.e., instead of investing upfront a lot of time in writing and verifying a complete specification, one can specify one-off properties in a few lines of Python and verify them without concern for the rest. We developed five representative NFs---a NAT, a Maglev load balancer, a MAC-learning bridge, a firewall, and a traffic policer---and verified with Vigor that they satisfy standards-derived specifications, are memory-safe, and do not crash or hang. We show that they provide competitive performance. The Vigor framework is available at http://vigor.epfl.ch.

ACM2019