TimeSys has published a second podcast on achieving rapid boots on Linux devices. “Fast boots — the sequel” discusses the relationship of footprint and boot time, post-2.6.15 kernels' CONFIG_EMBEDDED option, application pre-linking and profiling, filesystem selection, execute-in-place (XIP), and initramfs, among other interesting techniques.

The new podcast follows a similar podcast published two weeks ago. The original attracted considerable passionate feedback, according to moderaters Gene Sally and Maciej Halasz.

The two intrepid podcasters start out with a discussion of Matt Mackall's “Tiny-Linux” patchset, aimed at helping prune non-essential kernel functionalities. The patchset can be a “good starting point” when building fast-booting or small-footprint systems, according to Halasz. It was merged into the mainline kernel during the 2.6.15 release as the CONFIG_EMBEDDED option, shortly after Mackall was hired as principal developer by the Consumer Electronics Linux Forum (CELF).

Next, the podcast looks at optimizing application start-up time and performance, through pre-linking and application profiling.

Pre-linking, which is done at compile time, reduces application start-up times up to 30 percent, according to Halasz. Sally notes, “[A device is] not like a traditional desktop system: things are not going to shift around. You can safely [pre-link] applications, and still get some of the benefits of a shared library.”

Profiling, meanwhile, can work as a “second pair of eyes” to help developers understand where their applications are using time and CPU cycles. Profiling is also great for helping developers understand code that they did not write themselves — for example, helping them use APIs (application programming interfaces) more efficiently.

The pair next discuss various approaches to flash storage, including XIP (execute-in-place), an interesting technique in which kernel and applications are run in-situ from NOR flash, saving time that would otherwise be required to copy them into memory. Halasz cautions, “If your application is called very frequently, and links with other dynamic libraries, it may be better to keep it in RAM;” however, XIP is “one of the options definitely worth considering,” according to Sally.

These are only a sample of topics broached in the full 39-minute podcast. The podcast, along with several reference URLs, can be found here.

In other news, TimeSys recently published a brief guide about how to use its toolchains to build and rebuild Linux kernels. That interesting guide can be found here.

 
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