研究檔案同步操作的延遲時間對安卓應用程式反應時間的影響

Abstract

我們發現目前通用的安卓應用程式（Android Applications）在運作過程中，會發出很大量的檔案同步動作，我們相信此行為會直接或間接的影響到應用程式的執行流暢度亦或是執行時的反應時間長短。本研究是透過使用自動化以及量化的方式來量測檔案同步動作對應用程式執行流暢度以及反應時間的影響。我們量測的角度有二：執行時間以及畫面更新頻率。而我們在量測的過程中發現幾點與檔案同步操作息息相關的議題：(a) 應用程式的主線程或稱使用者介面線程被耗時的工作卡住。(b) 應用程式使用者介面線程與檔案讀寫線程存在相依性。(c) 檔案同步動作存在造成全域阻塞的可能性。我們發現在實驗結果的部分，回播時間上，使用加速檔案同步操作的檔案系統得到的時間改善較原始檔案系統少了17%之多。流暢度的部分，使用加速檔案同步操作的檔案系統在不可避免的application frame rate下降發生時，恢復正常的時間也較原始系統減少24%。

Android applications frequently call file synching operations, under which the application response becomes sluggish. This study aims at a quantitative approach of measuring how the performance of file synching has impact on application response. The impact is quantified in terms of application execution time and frame per second. We used three popular Android applications and measured their response under different file synching implementations, and we have three basic findings: (angel) An application could have its UI thread directly stuck by file synching operations, (beer) the UI thread of an application could depend on another thread that performed file synching operations, and (coffee) an application could be blocked when another application is doing file synching in background. We also found that an efficient fsync() implementation reduced the application execution by 17% and reduced the total less-than-target application frame rate time by 24%.