Dynamic occupancy grids (DOGs) have raised interest in the last years due to their ability to fuse information without explicit data association, to represent free space and arbitrary-shape objects and to estimate obstacles’ dynamics. Different works have presented strategies with demonstrated good performance. Most of them rely on LiDAR sensors, and some have shown that including additional velocity measurements enhance the estimation. This work aims at showing that velocity information can be directly inferred from objects displacement. Thus, a strategy using velocity feedback and its inclusion in the DOG is presented. The qualitative and quantitative analysis of results obtained from real data experimentation show a very good performance, specially in dynamic changing situations.

The Fuzzy Kalman Filter (FKF) was recently reformulated, with a number of basic examples included in order to demonstrate its applicability. We now look ahead to its practical implementation, introducing deep analysis which includes very detailed simulations and complete real applications. This will allow us to not only validate the FKF but also to draw important conclusions which will help users in the adjustment of the fuzzy filter parameters and the choosing of possibilistic distributions.

Memory bandwidth is a crucial resource in computing systems. Current CMP/SMT processors have a significant number of cores and they can run many threads concurrently. This large thread count adds high pressure to the memory bus, which demands high bandwidth to service memory requests from the cores. Hardware data prefetching is a well-known technique for hiding memory latency. Due to its speculative nature, however, in some situations prefetching does not effectively work, wasting memory bandwidth and polluting the caches. Data prefetching efficiency depends on the prefetching algorithm. It also depends on the characteristics of the applications running on the system. In this paper we propose an online bandwidth shifting mechanism that dynamically assigns bandwidth to applications according to their prefetch efficiency. This mechanism maximizes the utilization of memory bandwidth, thereby improving system performance and/or reducing memory power consumption. To the best of our knowledge, this solution is the first to not require hardware support. We evaluate the benefits of using our bandwidth shifting mechanism on a real system - the IBM POWER7. We obtain speedups in the order of 10-20% (in one instance, speedup exceeds 1.6X). Our mechanism does not generate a significant degree of unfairness among the applications. In many cases individual thread performance increases by 10-35%, while virtually no thread experiences a slowdown larger than 5%.

Accurately determining the energy consumed by each task in a system will become of prominent importance in future multicore-based systems because it offers several benefits, including (i) better application energy/performance optimizations, (ii) improved energy-aware task scheduling, and (iii) energy-aware billing in data centers. Unfortunately, existing methods for energy metering in multicores fail to provide accurate energy estimates for each task when several tasks run simultaneously. This article makes a case for accurate Per-Task Energy Metering (PTEM) based on tracking the resource utilization and occupancy of each task. Different hardware implementations with different trade-offs between energy prediction accuracy and hardware-implementation complexity are proposed. Our evaluation shows that the energy consumed in a multicore by each task can be accurately measured. For a 32-core, 2-way, simultaneous multithreaded core setup, PTEM reduces the average accuracy error from more than 12% when our hardware support is not used to less than 4% when it is used. The maximum observed error for any task in the workload we used reduces from 58% down to 9% when our hardware support is used.

Hardware data prefetch engines are integral parts of many general purpose server-class microprocessors in the field today. Some prefetch engines allow the user to change some of their parameters. The prefetcher, however, is usually enabled in a default configuration during system bring-up and dynamic reconfiguration of the prefetch engine is not an autonomic feature of current machines. Conceptually, however, it is easy to infer that commonly used prefetch algorithms, when applied in a fixed mode will not help performance in many cases. In fact, they may actually degrade performance due to useless bus bandwidth consumption and cache pollution. In this paper, we present an adaptive prefetch scheme that dynamically modifies the prefetch settings in order to adapt to the workload requirements. We implement and evaluate adaptive prefetching in the context of an existing, commercial processor, namely the IBM POWER7. Our adaptive prefetch mechanism improves performance with respect to the default prefetch setting up to 2.7X and 30% for single-threaded and multiprogrammed workloads, respectively.

Controlling power consumption and temperature is of major concern for modern computing systems. In this work we characterize thermal behavior and power consumption of an IBM POWER6-based system. We perform the characterization at several levels: application, operating system, and hardware level, both when the system is idle, and under load. At hardware level, we report a 25% reduction in total system power consumption by using the processor low power mode. We also study the effect of the hardware thread prioritization mechanism provided by POWER6 on different workloads and how this mechanism can be used to limit power consumption. At OS level, we analyze the power reduction techniques implemented in the Linux kernel, such as the tickless kernel and the CPU idle power manager. At application level, we characterize the power consumption and the temperature of two sets of benchmarks (METbench and SPEC CPU2006) and we study the effect of workload characteristics on power consumption and core temperature.

Microprocessor architectures have become increasingly power limited in recent years. Currently power and thermal envelopes dictate peak performance limits more than any other design constraint. As voltage scaling has slowed down, innovative techniques have been pursued to improve the power efficiency of the increasingly demanding multi-core architectures. In this paper we look at recent trends in multi-cores with a special focus on trends and techniques to address these challenges.