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603410053 603410099 Computer Science, National Chung Cheng University, 2014 Introduction A variation of the suspend-resume technique eliminates the need to initialize the Linux kernel, and when combined with approaches to enhance external memory read speed and shrink the suspend image, can decrease Android OS boot time by up to 90 percent. Our technique works well for any device that must frequently reboot with or without battery power. Shutting down power rather than putting the device in sleep mode can save battery life in devices such as mobile phones and tablet PCs; The technique is also robust against a rapid power loss for devices such as digital televisions. About This Paper Published in: Computer (Volume:47, Issue: 7 ) Date of Publication: July 2014 Sponsored by : IEEE Computer Society Publisher: IEEE U-BOOT FAST-BOOT Like the suspend-resume technique, U-Boot Fast-Boot includes suspend and resume processes. Unlike the suspend resume technique, U-Boot, which serves as the boot loader, reads the image directly after board initialization, eliminating the time normally needed to start the Linux kernel. Image data structure In our first attempt at using U-Boot Fast-Boots resume process, we could not use a memory map to restore pages because our technique does not initialize the kernel. As a result, the memory management unit (MMU) did not work. To enable mapping between saved images and the systems current state, we redesigned the image data format to the structure in Figure 1. Enhancing external memory read speed For external memory, we chose an SD card because of its popularity in embedded systems as additional external storage. We then accelerated the rate at which the U-Boot reads the suspend image from the SD card. Normally, U-Boot reads the image page by page from the SD card, at a data transfer rate of about 15 Mbytes per second on a class 4 SD card. Each page is stored to the appropriate page in RAM. To accelerate this rate, we modified the I/O operations in U-Boot and increased the amount of data transferred per transfer request, removing the overhead and additional associated latency. Our experiments showed that modification accelerated read speed from 15 to about 21 Mbytes per second, decreasing image read time by almost 30 percent and thus improving kernel start-up. Conclusions Feature Works To address that problem, we plan to research a new method that creates the suspend image only once when the system is first powered off and then uses this same suspend image to restore system state every power on. In the mean time, incremental steps can still reap benefits. Figure 5. You can use connector lines and arrows to visually guide viewers through your results. Adding emphasis this way is much, much better than making the point with words in the text section. These lines can help viewers read your poster even when youre not present. Shortening the Boot Time of Android OS Shrinking the suspend image The idea is to make the image as small as possible without compromising the systems ability to restore the system state. Stores least recently used pages of memory to swap pages on disk. Experiments show that this method reduces image size by about 50 to 70 percent. It takes some time to ensure that all pages are saved to the swap space and then to the SD disk. Consumers usually shut down their device and walk away, not waiting for the shutdown to complete. Storing the inactive pages in the swap space shifts some of the system restore time to shut-down time. Start-up time and image size comparison U-Boot Fast-Boot three inherent bottlenecks: Linux kernel initialization. Because the kernel is responsible for reading the image from disk, it must still be started after the boot loader, which takes approximately two to four seconds. Reading from external memory. The time to read the suspend image from disk depends on the external memorys read speed. Typically, an SD card reads approximately 10 Mbytes per second, so the method used to read the stored image is important. Large suspend image. A large image takes time to read, which lengthens the systems resume time.