Startup Time in the 21st Century: Filesystem Hacks and Assorted Tweaks

While processors have relentlessly increased in performance over the past few years, the amount of time it takes a modern Linux distribution to go from the bootloader to a working shell remains relatively large and painful. Several key points in the boot process offer the chance to make more efficient use of otherwise idle time in the system to perform tasks that are required by later stages of initialization. The missed opportunities range from the precious seconds lost while Grub idly awaits user input to the seek-bound thrashing of init scripts and filesystem checks.

To improve this situation, a block device cache called BootCache is filled via sequential reads earlier in the boot process. This helps remove the IO bottleneck from the boot process, enabling further performance tuning through traditional profiling techniques. This paper examines the impact of BootCache on startup time and regular workloads, as well as the new bottlenecks that are revealed by the modified system.

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