用於間歇性分散式嵌入式系統的併行控制方法

Abstract

智慧型的輕量分散式裝置所提供的應用已經在物聯網及無線感測網路等領域被大量使用，由於這些裝置的數量不斷成長，如何為這些裝置供電已成為關鍵挑戰。近年來，使用新興的能量攫取技術製成的自供電系統已成為替代電池的一項潛力替代方案。但由於些類能源本質上的不穩定，使得這樣的自供電系統呈現間歇運作的現象，因此也帶來在間歇運行下系統設計的挑戰。包括在間歇性運算下能實現並行運算、、非揮發性記憶體與處理器之間的資料一致性問題，及在分散式系統中，節點斷電導致整體性能下降的問題。我們首先採用了以時間序列為基礎的工作排程最佳化演算法，用以確保在分散式系統中併行工作的正確性。為了解決資料一致性問題，我們使用了可序列化驗證及分散式原子提交來保證提交的資料與處理器進度一致。接著我們分析間歇性在分散式系統中的行為，觀察節點斷電時可能導致的性能下降問題。並提出以替代資料來解決在資料存取上的性能下降問題。具體地說，該方法會在資料節點斷電時，自動尋找系統中其它有同樣資料的節點為替代。另外我們提出可累積式驗證提交，用以解決在驗證可序列化併行及提交改變時，節點斷電造成的效能下降。這個方法使得讓驗證及提交時的工作不會因為斷電而需要重做，以減少執行的時間。我自將這些設計在開源的即時作業系統上實作，並在實驗中增加最多百分之三十三的工作效率，以及降低百分之四十一的資料存取等待時間。

Internet of Things (IoT) devices are gradually adopting batteryless, energy harvesting solutions, thereby driving the development of an intermittent computing paradigm to accumulate computation progress across multiple power cycles. While many attempts have been made to enable standalone intermittent systems, less attention has focused on IoT networks formed by intermittent devices. We observe that the computation progress improved by distributed task concurrency in an intermittent network can be significantly offset by data unavailability due to frequent power failures. This paper presents an intermittentaware distributed concurrency control protocol which leverages existing data copies inherently created in the network to improve the computation progress of concurrently executed tasks. In particular, we propose a borrowingbased data management method to increase data availability and an intermittent twophase commit procedure incorporated with distributed backward validation to ensure data consistency in the network. The proposed protocol was integrated into a FreeRTOSextended intermittent operating system running on Texas Instruments devices. Experimental results across varied power sources and network sizes show that the computation progress can be significantly improved, and this improvement is more apparent under weaker power, where more devices will remain offline for longer duration.