  As we enter the era of domain-specific architectures, systems researchers
must understand the requirements of emerging application domains. Augmented and
virtual reality (AR/VR) or extended reality (XR) is one such important domain.
This paper presents ILLIXR, the first open source end-to-end XR system (1) with
state-of-the-art components, (2) integrated with a modular and extensible
multithreaded runtime, (3) providing an OpenXR compliant interface to XR
applications (e.g., game engines), and (4) with the ability to report (and
trade off) several quality of experience (QoE) metrics. We analyze performance,
power, and QoE metrics for the complete ILLIXR system and for its individual
components. Our analysis reveals several properties with implications for
architecture and systems research. These include demanding performance, power,
and QoE requirements, a large diversity of critical tasks, inter-dependent
execution pipelines with challenges in scheduling and resource management, and
a large tradeoff space between performance/power and human perception related
QoE metrics. ILLIXR and our analysis have the potential to propel new
directions in architecture and systems research in general, and impact XR in
particular. ILLIXR is open-source and available at https://illixr.github.io
