In the design of modern-day processors, energy consumption and fault tolerance have gained significant importance next to performance. This is caused by battery constraints, thermal design limits, and higher susceptibility to errors as transistor feature sizes are decreasing. However, achieving the ideal balance among them is challenging due to their conflicting nature (e.g., fault-tolerance techniques usually influence execution time or increase energy consumption), and that is why current processor designs target at most two of these axes. Based on that, we propose a new VLIW-based processor design capable of adapting the execution of the application at run-time in a totally transparent fashion, considering performance, fault tolerance, and energy consumption altogether, in which the weight (priority) of each one can be defined a priori. This is achieved by a novel decision module that dynamically controls the application's ILP to increase the possibility of replicating instructions or applying power gating. For an energy-oriented configuration, it is possible, on average, to reduce energy consumption by 37.2% with an overhead of only 8.2% in performance, while maintaining low levels of failure rate, when compared to a fault-tolerant design. ... Read more

Abstract—Multi-threaded applications execute their threads on different cores with their own local caches and need to share data among the threads. Shared caches are used to avoid lengthy and costly main memory accesses. The degree of cache sharing is a balance between reducing misses and increased hit latency. Dynamic caches have been proposed to adapt this balance to the workload type. Similarly, dynamic processors aim to execute workloads as efficient as possible to being able to balance between exploiting Instruction-level parallelism (ILP) and Thread-level parallelism (TLP). To support this, they consist of multiple processing components and caches that have adaptable interconnects between them. Depending on the workload characteristics, these can connect them together to form a large core that exploits ILP, or split them up to form multiple cores that can run multiple threads (exploiting TLP). In this paper, we propose a cache system that is able to further exploit this additional connectivity of a dynamic VLIW processor by being able to forward cache accesses to multiple cache blocks while the processor is running in multi-threaded (‘split’) mode. Additionally, only requests to global data are broadcasted, while accesses to local data are kept private. This will improve the hit rates similar to existing cache sharing schemes, but reduce the penalty due to stalling the other subcores. Local accesses are recognized by distinguishing memory accesses relative to the stack frame pointer. Results show that our cache exhibits similar miss rate reductions as shared caches (up to 90% and on average 26%), and reduces the number of broadcasted accesses by 21%. ... Read more