Patching up Network Data Leaks with Sweeper

Datacenters have witnessed a staggering evolution in networking technologies, driven by insatiable application demands for larger datasets and inter-server data transfers. Modern NICs can already handle 100s of Gbps of traffic, a bandwidth capability equivalent to several memory channels. Direct Cache Access mechanisms like DDIO that contain network traffic inside the CPU’s caches are therefore essential to effectively handle growing network traffic rates. However, a growing body of work reveals instances of a critical DDIO weakness known as “leaky DMA”, occurring when a significant fraction of network traffic leaks from the CPU’s caches to memory. We find that such network data leaks cap the network bandwidth a server can effectively utilize. We identify that a major culprit for such network data leaks are evictions of already consumed dirty network buffers. Our key insight is that buffers already consumed by the application typically need not be written back to memory, as their next reuse will be a full overwrite with new network data by the NIC. We introduce Sweeper, a hardware extension and API that allows applications to mark such consumed network buffers. Hardware then skips writing marked buffers back to memory, drastically reducing memory bandwidth consumption and mitigating the performance penalty of network data leaks. Sweeper boosts a 24-core server’s peak sustainable network bandwidth by up to $2. 6 \times$ as compared to DDIO-based configurations.