kqueue versus epoll: A Performance Comparison

Shrikant Giridhar
Cindy Zhang

Abstract

Modern high-performance webserver architectures often use an event
driven concurrency model for flexibility and performance reasons.
These server architectures have evolved over time from using a
single-threaded implementation us- ing events to a hybrid model using
a combination of event notifications and worker thread pools to handle
potentially blocking requests.  As web applications grow in popularity
and server workloads become more diverse, scalability has become an
important design aspect for industrial servers. Kernel vendors have
responded to the scalability limitations of traditional event
notification system calls by introducing their own flavors of scalable
notification mechanisms - epoll in Linux and kqueue in BSD derived
distributions.  In this paper, we discuss the architecture of these
system calls and evaluate their real-world performance using a popular
high-performance webserver (node.js) on Linux and FreeBSD. In doing
so, we also compare their claims of scalability against POSIX I/O
notification calls - select and poll based on previous literature and
using a set of macro and micro benchmarks of our own.