Observing the Invisible: Live Cache Inspection for High-Performance Embedded Systems

TL;DR

This paper introduces CacheFlow, a Linux kernel module that enables live inspection of CPU cache contents on embedded systems, providing new insights into cache behavior without external hardware.

Contribution

The paper presents a novel method for live cache inspection using vendor-provided interfaces, enhancing understanding of cache dynamics in embedded systems.

Findings

Enables real-time cache snapshotting on embedded hardware

Improves understanding of cache evolution and behavior

Complements existing cache profiling techniques

Abstract

The vast majority of high-performance embedded systems implement multi-level CPU cache hierarchies. But the exact behavior of these CPU caches has historically been opaque to system designers. Absent expensive hardware debuggers, an understanding of cache makeup remains tenuous at best. This enduring opacity further obscures the complex interplay among applications and OS-level components, particularly as they compete for the allocation of cache resources. Notwithstanding the relegation of cache comprehension to proxies such as static cache analysis, performance counter-based profiling, and cache hierarchy simulations, the underpinnings of cache structure and evolution continue to elude software-centric solutions. In this paper, we explore a novel method of studying cache contents and their evolution via snapshotting. Our method complements extant approaches for cache profiling to better formulate, validate, and refine hypotheses on the behavior of modern caches. We leverage cache introspection interfaces provided by vendors to perform live cache inspections without the need for external hardware. We present CacheFlow, a proof-of-concept Linux kernel module which snapshots cache contents on an NVIDIA Tegra TX1 SoC (system on chip).