M.Sc Thesis

M.Sc StudentWalter Isask'har
SubjectQuality of Service in Network on-Chip
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROFESSOR EMERITUS Israel Cidon


Network on Chip (NoC) has been proposed for future SoC interconnect. Hotspots are SoC modules which occasionally receive traffic that exceeds the rate at which they can absorb data. Hotspots are common in real-life SoCs, where external DRAM or internal components (caches, CAMs, special purpose processors) are bandwidth limited and in high demand by other units. While hotspots are commonly dealt with in store-and-forward networks, they have dire consequences in wormhole networks in terms of reducing overall network efficiency and unfair allocation of the scarce resources.

In this work we demonstrate that hotspot modules on wormhole-based NoCs dramatically reduce network efficiency and unfairly allocate system resources, showing that a single hotspot may ruin the performance of the entire NoC. We examine the source fairness problem and the effect hotspot congestion has on traffic not destined at the hotspot module. By using simulations, we show the severity of both problems in a general wormhole network. In order to resolve these problems, we introduce a novel low-cost end-to-end credit-based resource allocation technique that regulates access to the hotspot module. Simulations are then used again in order to show that this low cost hardware mechanism achieves significant improvement in the system's performance.

In addition, the problem of assigning QNoC links bandwidth is also addressed. A greedy capacity allocation algorithm that uses a novel delay analysis is formulated, and the potential benefit is shown using design examples.