XDP and AF_XDP provide a high-performance mechanism for driver-layer packet processing and zero-copy delivery of packets into userspace, while maintaining access to standard kernel networking constructs — capabilities that distinguish them from full kernel-bypass frameworks such as DPDK. However, the current AF_XDP implementation offers no efficient in-kernel mechanism for forwarding packets between AF_XDP sockets in a zero-copy manner. Because AF_XDP operates without the conventional full network stack socket abstraction, even basic localhost redirection requires an external switch or additional hardware-assisted NIC capabilities, limiting both performance and usability.

In this talk, we introduce FLASH, an extension to the AF_XDP subsystem that enables low-overhead, in-kernel packet transfer between AF_XDP sockets. FLASH provides zero-copy delivery for sockets that share a memory area and a fast single-copy datapath for sockets backed by independent memories. The design incorporates several performance-oriented mechanisms, including smart blocking with backpressure for congestion handling and an adaptive interrupt-to-busypoll transition to reduce latency under load.

We demonstrate that co-located applications using AF_XDP can leverage FLASH to achieve up to 2.5× higher throughput compared to SR-IOV-based approaches, while preserving the programming model and flexibility of the XDP/AF_XDP ecosystem. The talk will also outline future directions and how this technique can be applied across different use cases like DDoS mitigation, load balancing, etc.





Github link - https://github.com/networkedsystemsIITB/flash