ADAM: Adaptive Block Placement with Metadata Embedding for Hybrid Caches

Spin-Transfer Torque Random Access Memory (STT-RAM) is a potential alternative for SRAM-based on-chip caches. STT-RAM offers high density and low leakage power, thereby can be used to build a large capacity last-level caches (LLC). Unfortunately, the write latency of the STT-RAM is significantly longer, and its write energy is considerably higher compared to SRAM. To mitigate these concerns, researchers have proposed hybrid caches that are comprised of SRAM and STT-RAM regions. In such hybrid caches, an intelligent block placement policy is necessary to store as many write-intensive blocks in the SRAM region. This paper proposes an adaptive block placement framework with metadata embedding (ADAM) for hybrid caches. ADAM embeds metadata (i.e., write-intensity) into a cache block when it is evicted from LLC. When a cache block is brought from the main memory, metadata embedded in the block is extracted and used to determine the write-intensity of the block. Our evaluation shows that ADAM can improve performance by 26 % (on average) over a baseline block placement scheme.