QuARK: Quality-configurable approximate STT-MRAM cache by fine-grained tuning of reliability-energy knobs

Emerging STT-MRAM memories are promising alternatives for SRAM memories to tackle their low density and high static power consumption, but impose high energy consumption for reliable read/write operations. However, absolute data integrity is not required for many approximate computing applications, allowing energy savings with minimal quality loss. This paper proposes QuARK, a hardware/software approach for trading reliability of STT-MRAM caches for energy savings in the on-chip memory hierarchy of multi- and many-core systems running approximate applications. In contrast to SRAM-based cache-way-level actuators, QuARK utilizes fine-grained cache-line-level actuation knobs with different levels of reliability for individual read and write accesses which are unique to STT-MRAM and suitable for systems running multiple applications with mixed accuracy sensitivity, thus avoiding interapplication actuation interference. Our experimental results with a set of recognition, mining and synthesis (RMS) benchmarks demonstrate up to 40% energy savings over a fully-protected STT-MRAM cache, with negligible loss in the quality of the generated outputs.