Analytical Modeling the Multi-Core Shared Cache Behavior with Considerations of Data-Sharing and Coherence

To mitigate the ever worsening Power wall and Memory wall problems, multi-core architectures with multilevel cache hierarchies have been widely used in modern processors. However, the complexity of the architectures makes the modeling of shared caches extremely complex. In this paper, we propose a data-sharing aware analytical model for estimating the miss rates of the downstream shared cache in a multi-core environment. Moreover, the proposed model can also be integrated with upstream cache analytical models with the consideration of multi-core private cache coherent effects. The integration avoids time-consuming full simulations of the cache architecture, which are required by conventional approaches. We validate our analytical model against gem5 simulation results under 13 applications from PARSEC 2.1 benchmark suites. We compare the L2 cache miss rates with the results from gem5 under 8 hardware configurations including dual-core and quad-core architectures. The average absolute error is less than 2% for all configurations. After integrated with the upstream model, the overall average absolute error is 8.03% in 4 hardware configurations. As an application case of the integrated model, we also evaluate the miss rates of 57 different cache configurations in multi-core and multi-level cache scenarios.Comment: The manuscript has been submitted to Microprocessors and Microsystem

Fast Modeling L2 Cache Reuse Distance Histograms Using Combined Locality Information from Software Traces

To mitigate the performance gap between CPU and the main memory, multi-level cache architectures are widely used in modern processors. Therefore, modeling the behaviors of the downstream caches becomes a critical part of the processor performance evaluation in the early stage of Design Space Exploration (DSE). In this paper, we propose a fast and accurate L2 cache reuse distance histogram model, which can be used to predict the behaviors of the multi-level cache architectures where the L1 cache uses the LRU replacement policy and the L2 cache uses LRU/Random replacement policies. We use the profiled L1 reuse distance histogram and two newly proposed metrics, namely the RST table and the Hit-RDH, that describing more detailed information of the software traces as the inputs. For a given L1 cache configuration, the profiling results can be reused for different configurations of the L2 cache. The output of our model is the L2 cache reuse distance histogram, based on which the L2 cache miss rates can be evaluated. We compare the L2 cache miss rates with the results from gem5 cycle-accurate simulations of 15 benchmarks chosen from SPEC CPU 2006 and 9 benchmarks from SPEC CPU 2017. The average absolute error is less than 5%, while the evaluation time for each L2 configuration can be sped up almost 30X for four L2 cache candidates.Comment: This manuscript has been major revised and re-submitted to Journal of Systems Architectur

An Analytical Model for Performance and Lifetime Estimation of Hybrid DRAM-NVM Main Memories

NVMs have promising advantages (e.g., lower idle power, higher density) over the existing predominant main memory technology, DRAM. Yet, NVMs also have disadvantages (e.g., limited endurance). System architects are therefore examining hybrid DRAM-NVM main memories to enable the advantages of NVMs while avoiding the disadvantages as much as possible. Unfortunately, the hybrid memory design space is very large and complex due to the existence of very different types of NVMs and their rapidly-changing characteristics. Therefore, optimization of performance and lifetime of hybrid memory based computing platforms and their experimental evaluation using traditional simulation methods can be very time-consuming and sometimes even impractical. As such, it is necessary to develop a fast and flexible analytical model to estimate the performance and lifetime of hybrid memories on various workloads. This paper presents an analytical model for hybrid memories based on Markov decision processes. The proposed model estimates the hit ratio and lifetime for various configurations of DRAM-NVM hybrid main memories. Our model also provides accurate estimation of the effect of data migration policies on the hybrid memory hit ratio, one of the most important factors in hybrid memory performance and lifetime. Such an analytical model can aid designers to tune hybrid memory configurations to improve performance and/or lifetime. We present several optimizations that make our model more efficient while maintaining its accuracy. Our experimental evaluations show that the proposed model (a) accurately predicts the hybrid memory hit ratio with an average error of 4.61% on a commodity server, (b) accurately estimates the NVM lifetime with an average error of 2.93%, and (c) is on average 4x faster than conventional state-of-the-art simulation platforms for hybrid memories