適用於三維晶片內網路之熱管理機制

Abstract

本論文將研究三維晶片內網路(3D Network-on-Chip)中的溫度議題。隨著製程演進，晶片內網路成為多核心平台晶片內通訊的常用架構。而結合三維積體電路技術後，三維晶片內網路更具有高整合密度、提升網路頻寬、降低連線延遲與功耗等好處。但當晶片內網路建置在三維積體電路環境時，溫度問題將會比二維晶片內網路更加嚴重。三維積體電路在相同面積下將堆疊數倍的晶粒，因此將造成功率密度急遽增加與各層散熱能力不同等問題。此外，在三維積體電路系統中，網路所造成的溫度跟處理器所造成的溫度皆是造成晶片溫度上升的主要來源。因此晶片內網路所造成的溫度是不可忽視的。傳統在二維晶片內網路之熱處理機制若直接延伸至三維晶片內網路的環境中會造成熱流過小而無法順利運作。在本論文中，我們提出了一個「交通感知向下路由演算法(Traffic-aware downward routing algorithm)」，其考量了三維積體電路之異質散熱特性，使空間溫度平衡，在一般情況下不影響效能並降低網路溫度。因此在溫度限制下，向下路由演算法將比傳統路由演算法提供更加的網路效能。另外，我們提出了一個「溫度感知垂直節流技術(Thermal-aware vertical throttling technique)」，其對晶片內網路之溫度監測，在溫度過高時，藉由調整路由器之交通量，使熱點到熱沉間形成散熱路徑，能夠及時把熱點降溫，使時間上溫度平衡並防止溫度過高所導致之網路有效性(availability)下降。我們的實驗結果顯示，向下路由演算法在一般溫度限制下，可以使得網路最大吞吐率(throughput)提升12%。而網路在沒有垂直節流技術下，有效性將嚴重下降。若具有垂直節流技術，在一般溫度限制下，可以使得網路有效接受封包率(available received packet rate)維持在至少60%。因此，對於三維晶片內網路，我們的技術可以達到在一般情況下不影響效能並降溫，且在溫度過高時予以控制，維持系統有效性。

In this thesis, we focus on the thermal problems in 3D Network-on-Chips (NoC). As process scales down, the NoC becomes the popular architecture of on-chip communication in Chip MultiProcessors (CMP) platforms. With 3D IC techniques, 3D NoC can perform higher integrated density, higher network bandwidth, lower interconnection delay, and lower power consumption than 2D NoC. If the NoC is established in the environment of 3D ICs, the thermal problem is more serious than 2D NoC. Many dies stacked up in 3D ICs result in the problems of power density increasing drastically, and different heat dissipations in different layers. Besides, both heats of networks and heats of CPUs are the major reasons that cause temperatures increasing in 3D NoC. Hence, the heats from NoC cannot be ignored. Thermal management techniques in traditional 2D NoC cannot extend to 3D NoC directly. Therefore, thermal management schemes for 3D NoC are needed. In this thesis, a Spatial Thermal Distribution Balancing (STDB) traffic-aware downward routing algorithm is proposed which considers the thermal characteristic of 3D NoC, balances the spatial thermal distribution, and reduced temperature with less performance impact. Besides, a Temporal Thermal Distribution Balancing (TTDB) thermal-aware vertical throttling technique is proposed which monitors the network temperature, controls the traffic in hotspot router, forms the heat flow to heat sink, and prevents from overheating. Experiments show that under the normal thermal limit, the maximum network throughput using the STDB scheme can be improved by 12% than using the general XYZ routing. Besides, the TTDB scheme has the higher received packet rate comparing to the distributed throttling. Under the Markov-Modulated Process (MMP) traffic model, the available received packet rate is at least 60%. Therefore, for 3D NoC, the proposed techniques can reduce temperature with less performance impact in general condition and prevent overheating with less packet loss comparing to traditional techniques.