Memory-manager/Scheduler Co-design: Optimizing Event-driven Programs to Improve Cache Behavior

International audienceEvent-driven programming has emerged as a standard to implement high-performance servers due to its flexibility and low OS overhead. Still, memory access remains a bottleneck. Generic optimization techniques yield only small improvements in the memory access behavior of event-driven servers, as such techniques do not exploit their specific structure and behavior. This paper presents an optimization framework dedicated to event-driven servers, based on a strategy to eliminate data-cache misses. We propose a novel memory manager combined with a tailored scheduling strategy to restrict the working data set of the program to a memory region mapped directly into the data cache. Our approach exploits the flexible scheduling and deterministic execution of event-driven servers. We have applied our framework to industry-standard web servers including TUX and thttpd, as well as to the Squid proxy server and the Cactus QoS framework. Testing TUX and thttpd using a standard HTTP benchmark tool shows that our optimizations applied to the TUX web server reduce L2 data cache misses under heavy load by up to 75% and increase the throughput of the server by up to 38%