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This article shows you what is the way to make the Linux system boot faster, the content is concise and easy to understand, it will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

Of all the computers I own or use, the one that starts fastest is the one from the 1980s. By the time you move your hand from the power key to the keyboard, the BASIC interpreter is already waiting for you to enter commands. For modern computers, startup time ranges from 15 seconds for laptops to a few minutes for small home servers. Why are their startup times different?

The 1980s microcomputer, which booted directly to the BASIC command line prompt, had a very simple CPU that started fetching and executing instructions from a memory address as soon as it was powered on. Because the BASIC of these systems is in ROM, it takes little time to load-- you'll soon be at the BASIC command prompt. More complex contemporary systems, such as IBM PC or Macintosh, take a considerable amount of time to boot (about 30 seconds), although this is mainly due to the need to read the operating system from the floppy disk. Only a small part of the time is spent on firmware before the operating system can be loaded.

Modern servers often spend minutes rather than seconds on firmware before reading the operating system from disk. This is mainly due to the increasing complexity of modern systems. CPU is no longer able to execute instructions at full speed just to run, we are used to CPU frequency changes, energy-saving standby, and CPU multicore. In fact, there are a surprising number of simpler processors within modern CPU that assist the main CPU core to boot and provide run-time services, such as suppressing frequency when it is overheated. In most CPU architectures, the code running on these cores within your CPU is provided in the form of opaque binary blob.

On OpenPOWER systems, all instructions running in each core within CPU are open source. On machines with OpenBMC (such as IBM's AC922 system and Raptor's TALOS II and Blackbird system), this also extends to the code running on the substrate management controller Baseboard Management Controller. This means that we can find out why it took so long from plugging in the power cord to showing a familiar login interface.

If you are a member of a kernel-related team, you may have started many kernels. If you are part of a firmware-related team, you may have to boot many different firmware images, followed by an operating system to make sure your firmware still works. If we can reduce the startup time of the hardware, these teams can be more productive, and end users will be grateful when setting up the system or rebooting to install firmware or system updates.

Over the past few years, the launch time of Linux distributions has been improved a lot. Modern initialization systems do a good job of handling parallel and on-demand tasks. On a modern system, once the kernel starts executing, it can enter the login prompt interface in just a few seconds. Just a few seconds here is not the place to optimize startup time, we need to get to an earlier place: before we get to the operating system.

On OpenPOWER systems, firmware loads the operating system by booting a Linux kernel stored on a firmware flash memory chip. It runs a user-mode program called Petitboot to find the disk on which the user wants to boot and boot it through kexec. With these optimizations, starting the Petitboot environment takes up only a few percent of the startup time, so we have to look for optimizations elsewhere.

Before the Petitboot environment starts, there is a pilot firmware called Skiboot, and there is a Hostboot before it. Before Hostboot is Self-Boot Engine, a separate core on a wafer slice (die), which starts a single CPU core and executes instructions from the Level 3 cache. These components are a major part of the progress we can make in reducing startup time because they take most of the time to start. Maybe some of these components are not sufficiently optimized or as parallel as possible?

Another research path is the restart time rather than the startup time. Do we really need to reinitialize all the hardware when rebooting?

As with any modern system, solutions to improve startup (or restart) time have become a combination of more parallel execution, solving legacy problems, and (arguably) cheating.

The above is what is the way to make the Linux system boot faster? have you learned the knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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