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To accommodate the growing demand for memory capacity in a cost-effective way, multiple types of memory are incorporated in a single system. In such tiered memory systems consisting of small fast and large slow memory components, accurately identifying the performance importance of pages is critical to properly migrate hot pages to fast memory. Meanwhile, growing address translation cost due to the increasing memory footprints, helped adopting huge pages in common systems. Although such page hotness identification problems have existed for a long time, this paper revisits the problem in the new context of tiered memory systems and huge pages. This paper first investigates the memory locality behaviors of applications with three potential migration polices, least-recently-used (LRU), least-frequentlyused (LFU), and random with huge pages. The evaluation shows that none of the three migration policies excel the others, as the effectiveness of each policy depends on application behaviors. In addition, the results show huge pages can be effective even with page migration, if a proper migration policy is used. Based on the observation, this paper proposes a novel dynamic policy selection mechanism, which identifies the best migration policy for a given workload. It allows multiple concurrently running workloads to adopt different policies. To find the optimal one for each workload, this study first identifies key features that must be inferred from limited approximate memory access information collected using accessed bits in page tables. In addition, it proposes a parallel emulation of alternative policies to assess the benefit of possible alternatives. The proposed dynamic policy selection can achieve 23.8% performance improvement compared to a prior approximate mechanism based on LRU lists in Linux systems.

For optical crossconnect and packet switched applications based on fast wavelength switching of distributed Bragg reflector (DBR) lasers, the wavelength switching delay is an important device characteristic. A large-signal model for a three-section DBR laser is described which permits evaluation of the intramodal and intermodal wavelength switching delay. The steady-state mode spectrum and loss obtained from a transmission line model of the laser are used in modified multimode rate equations to explicitly include the device structure and operating conditions in the dynamic model. Mode competition is shown to cause the intermodal wavelength switching delay to increase significantly as the destination wavelength approaches the edge of a mode tuning curve. The same behaviour is observed experimentally. >

Numerical calculations of the frequency modulation responses of monolithically integrated external-cavity semiconductor lasers are performed using G.P. Agrawal's (J. Appl. Phys., vol.56, p.3110-15, 1984) two-section model. Theoretical results show good agreement with the reported experimental results. The comparison of the modulation responses of the solitary semiconductor laser diodes, the conventional external-cavity semiconductor lasers, and the integrated passive external-cavity semiconductor lasers demonstrates that the integrated external-cavity semiconductor laser is the best choice for use in direct frequency modulation. >