Extended performance analysis of the time predictable on-demand coherent data cache for multi- and many-core systems
Arthur Pyka, Mathias Rohde, Sascha Uhrig · 2014
Powerful cache systems are required in multi- and many-core systems in order to provide a suitable performance. Moreover, these caches must provide coherent accesses to shared data. With respect to embedded real-time systems, traditional write-invalidate and write-update coherence protocols hamper a static worst case execution time analysis, since the content and state of a local cache can be modified by other cores. Hence, a meaningful cache analysis is no more possible. In previous work, we introduced the On-Demand Coherent Cache (ODC2) which provides coherent accesses to shared data without any coherence transactions and without modifications of other caches. It allows a tight worst case execution time (WCET) analysis at4 the expense of a decreased hit rate and an additional write-back procedure. In this work, we briefly describe two versions of the ODC2before we present detailed evaluations of its performance and the cost of time predictability. We quantify the overhead of the writeback procedure of one of ODC2's variations and we estimate the impact on the hit rate.