Libra: Accelerating Socket I/O via Programmable Selective Data Copying

TL;DR

Libra is an OS-level framework that reduces data copying in socket I/O by selectively copying only metadata, significantly improving throughput and latency for cloud-native proxies without modifying existing applications.

Contribution

Libra introduces a novel eBPF-based selective-copy mechanism that preserves socket semantics and improves performance in unmodified proxies.

Findings

Up to 4.2x increase in plaintext throughput

Over 90% reduction in P99 tail latency

2.0x throughput boost with hardware-offloaded kTLS

Abstract

Layer-7 (L7) proxies are critical to modern cloud-native systems, yet their performance is increasingly bottlenecked by copying entire payloads across the kernel-user boundary. Existing approaches reduce this overhead but typically sacrifice compatibility with unmodified POSIX applications, introduce new APIs, or require specialized environments. We show that, under conventional OS abstractions, fully eliminating kernel-user copies while preserving standard socket semantics for unmodified proxies is fundamentally impossible. This leads to a practical insight: in common L7 workloads, proxies inspect only small metadata (e.g., HTTP headers) for routing, while forwarding the bulk payload unchanged. Based on this insight, we present Libra, an OS-level selective-copy framework that copies only metadata to the user space and retains the bulk payload in the kernel for forwarding, reducing data movement without breaking compatibility. Libra uses eBPF to identify protocol-specific metadata boundaries and coordinate selective copy and payload reuse across receive and transmit paths, all without modifying the socket API. Implemented in Linux and evaluated with unmodified Nginx and HAProxy, Libra improves plaintext throughput by up to 4.2x and reduces P99 tail latency by over 90%. With hardware-offloaded kTLS, it boosts encrypted throughput by 2.0x and cuts tail latency by 65%.