利用實驗分析加速嵌入式Linux 2.6.14核心的開機時間

Abstract

在本篇論文中，我們嘗試利用實驗性的分析方法降低嵌入式Linux 2.6.14核心的開機時間，並且採用內建德儀OMAP5912核心的開發套件作為實驗平台。首先我們分析核心的開機流程，接著使用示波器與邏輯分析儀測量整個開機流程中每一個函式區塊的時間需求。根據所收集到的時間量測資料，我們選擇執行時間較長的部分，研究與其相關的U-Boot、Linux核心以及BusyBox原始碼，最後判斷該部分的操作是否可以在經過修改程式碼之後被簡化或是甚至在沒有副作用的情況下略過。在初步的結果裡，我們已經確認在開機流程中有許多項目是可以加以修訂來加速開機時間。實驗結果顯示，利用我們所提出的核心設定以及最佳化方法，我們可以在使用U-Boot 1.1.3、Linux2.6.14核心與BusyBox 1.01的OMAP5912平台上將整體開機時間由原本的7934.41毫秒大幅減少到1477.77毫秒。而如此的快速開機是眾多嵌入式系統所需要的重要特性。

In this thesis, we try to minimize the boot time of the embedded Linux 2.6.14 kernel with the empirical approaches. For the experimental purpose, TI’s ARM9-based OMAP5912 development kit is selected as our reference platform. Firstly, we analyze the boot sequence of the selected kernel and measure the time needed for each functional block in the whole sequence using the oscillator and logical analyzer. With the collected timing data, we hack in the related codes of U-Boot, Linux kernel and BusyBox that expose long execution time and study whether they can be either simplified by rewriting the codes or even skipped without any side effect. As a preliminary result, we have identified several points in the boot sequence that can be reworked to achieve faster boot time. In our experiment on the reference platform and with our suggested kernel configuration, we have achieved the instant boot of U-Boot 1.1.3, Linux kernel 2.6.14 and BusyBox 1.01 by greatly reducing the total boot time from 7934.41 ms to 1477.77 ms which is considered as one of the important features on many embedded systems.