Disable Console

Description
You can save time during kernel bootup by disabling the console output. The easiest way to do this is to use the "quiet" option on the kernel command line (described below).

Printk output is usually directed to a serial port or a VGA console during bootup. By disabling console output, the time taken to output the characters (and perform things like software scrolling of the display buffer) is eliminated.

How to implement or use
To disable console output during kernel bootup, use the "quiet" option on the kernel command line.

To do this, just put the word "quiet" (without the quotes) in the kernel command line, with no other arguments. This will suppress printk output during booting. Note that printk messages are still buffered in the kernel and can be retrieved after booting using the "dmesg" command.

Expected Improvement
This saves time during kernel bootup by suppressing printk output. Printk output delays depend on a number of factors, but in the use cases cited below, the savings were in the range of a few hundred milliseconds.

With a serial console, the time to output characters is dependent on the serial port speed. However, with a VGA console, the time to output the characters is dependent on the speed of the processor. Therefore, the slower your processor, the more savings you will gain from this technique.

Projects
None

Specifications
None

Patches
None

Case 1
From data submitted by Maruyama Kiyoyasu of Mitsubishi.

Case 2
From data submitted by Noboru Wakabayashi of Hitachi.