Characterization of Context Switch Effects on L2 Cache

EKER, ABDULAZIZ. Characterization of Context Switch Effects on L2 Cache. (Under the direction of Dr. Yan Solihin.) Multitasking is common in most systems. In order to use the processor resources efficiently, a multitasking system schedules processes to run for certain intervals by switching (saving and restoring) their contexts. However, since processes bring their own data to the cache when they are running, context switching causes each process to suffer from more cache misses. The behavior of L2 cache misses due to context switches activities under different cache configurations, working-set sizes, and process priorities has not been sufficiently investigated. Analysis of this behavior will give insights about the reasons and ways to mitigate these misses. The first contribution of this paper is the characterization of how context switch misses at the L2 cache is affected by process priorities. The paper also characterizes the context switch effect with various cache configurations, including the size and associativity of the cache. Finally, it defines two types of misses that occur due to context switches. Replacement context switch misses occur when a process’ working set is replaced by an interfering process. Reorder context switch misses occur due to reordering of lines by an interfering process, i.e. moving lines from more recently used to less recently used position. Through the characterization, we found that the number of context switch misses significantly increases with lower priorities. On average, on a Linux operating system, a process with the lowest priority suffers 15.4× more L2 cache misses due to the context switch effect compared to when time-sharing is not used, while the process with a relatively higher priority suffers only 1.2× more misses. In addition, we observed that the impact of context switch is affected more by the priority of the process itself, rather than the priority of the interfering process. We also observed that reorder context switch misses increase with higher associativity. Finally, the context switch effect is strongest when a process’ working set size is close to the cache size. Characterization of Context Switch Effects on L2 Cache