一種在 Xen 上基於 SDL 的有效率顯示機制

Abstract

隨著使用者端虛擬化越來越盛行，顯示相關的虛擬化技術近年來在虛擬化軟體和虛擬化硬體指令的支援下蓬勃發展。Xen 是一套提供虛擬化的軟體，它支援了 VGA 派送 (Pass-through) 技術，可以將實體顯示卡指定給任何一個全虛擬機器，大幅度改善該虛擬機器的顯示效能。SDL 是一套跨平台多媒體函式庫，常用來存取系統底層的資訊；開啟了 VGA 派送後，傳統在 Xen 上基於 SDL 的顯示機制卻無法正常運作，因為該機制只支援由特定虛擬機器來控管實體顯示卡。有鑑於此，我們利用共享記憶體設計並實作一套基於 SDL 新的顯示機制。這套機制特別在於當實體顯示卡派送給某一全虛擬化機器使用後，它還是可以很有效率地支援顯示使用者端各虛擬機器的桌面。本論文比較多種不同的顯示機制，並由實驗結果驗證我們提出的顯示機制有較穩定的畫面更新頻率且使用較低的系統資源。所以，這套新的顯示機制可以在虛擬化的使用者端環境下，以更好的效能取代傳統的顯示機制。

As client-side virtualization becomes more popular, lots of display related technologies for virtualization have also been developed with the advance of virtualized software and hardware support. Xen is a software supporting virtualization with a feature called VGA pass-through to directly assign the physical VGA device to any fully-virtualized virtual machine and significantly improve the display performance of the virtual machine; whereas SDL is a cross-platform multimedia library, usually used to access low-level system information. However, after the VGA pass-through is turned on, the original SDL-based display mechanism on Xen cannot work properly because it only supports that the physical VGA device is controlled by a specific virtual machine. Therefore, we design and implement a new SDL-based display mechanism with shared memory so that, after the physical VGA device is passed through to some virtual machine, our mechanism still can display the desktop of any other virtual machine efficiently. This thesis then compares several display mechanisms and the experimental results verify that our mechanism provides more stable refresh rate with lower CPU usage. As a result, our new SDL-based display mechanism can replace the original one used in the client-side virtualized environment with better performance.