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#1 2010-07-30 17:38:48

DrPhil
Member
Registered: 2010-07-30
Posts: 4

[SOLVED]What is fastest? MOD_AUTOLOAD="yes" or MOD_AUTOLOAD="no"

Hello Arch users!

I have installed Arch just a few days ago, and now when the easy stuff (X, Gnome) is done I need some help.
I've read a lot of articles on the very excellent wiki, and gathered great knowledge, now I want to start learn
more about tweaking and changing the things that are a little more difficult.

I've read about the Arch boot process and lots and lots of other things. What I want to know is which way is preferred:

MOD_AUTOLOAD="yes"
MODULES=(ndiswrapper nvidia fuse !snd-mixer-oss !snd-pcm-oss)

or

MOD_AUTOLOAD="no"
MODULES=(ndiswrapper button fan processor thermal cdrom agpgart ... (LOTS OF MODULES HERE) ... sd_mod sr_mod st)

The wiki says that autoloading should be slower (Rc.conf#Hardware, Hwdetect#Example) but in the Udev article this is written:

udev loads kernel modules simultaneously, which can provide a speed increase during bootup.

To make sure what was the truth I actually tried and added the modules needed (hwdetect --modules) and disabled the autoloading of modules. The test told me that disabling autoloading made my boot time 1-2 seconds slower. I am sure that I load a few unnecessary modules. As an example, floppy was added by hwdetect although I do not have anything to read floppies with on the computer.

Should I use autoloading or not? Why?
Can I make a significant improvement of my boot time by removing unnecessary modules?

Thank you for your help, and if my questions is clearly answered somewhere else, you can just provide a link. smile


(Bonus question: if I have MOD_AUTOLOAD="no" and have a blacklisted module, will I get the same result as if I remove it from the list?)

Last edited by DrPhil (2010-07-30 19:48:10)

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#2 2010-07-30 18:33:54

litemotiv
Forum Fellow
Registered: 2008-08-01
Posts: 5,026

Re: [SOLVED]What is fastest? MOD_AUTOLOAD="yes" or MOD_AUTOLOAD="no"

Welcome to the forums DrPhil.

There are a few threads on these forums about decreasing boot time, i suggest you check them out. Here is one: Quick-init - Boot your arch in 10 seconds

There is also a wiki page dedicated to it: Tweaking for a faster boot time


ᶘ ᵒᴥᵒᶅ

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#3 2010-07-30 19:22:51

Misfit138
Misfit Emeritus
From: USA
Registered: 2006-11-27
Posts: 4,189

Re: [SOLVED]What is fastest? MOD_AUTOLOAD="yes" or MOD_AUTOLOAD="no"

The way that paragraph was written was confusing, and you were falsely led to believe that there was a contrast that really didn't exist.
I have updated the language in that article to more accurately describe udev's module loading.

udev loads kernel modules simultaneously, which can provide a speed increase during bootup...

^That is the phrase which got us into trouble. It now reads:

udev loads kernel modules by utilizing coding parallelism to provide a potential performance advantage versus loading these modules serially. The modules are therefore loaded asynchronously. The inherent disadvantage of this method is that udev does not always load modules in the same order on each boot. If the machine has multiple block devices, this may manifest itself in the form of device nodes changing designations randomly. For example, if the machine has two hard drives, /dev/sda may randomly become /dev/sdb. See below for more info on this.

fwiw

Just don't confuse udev loading modules in parallel with specifying them in rc.conf...
Apples and oranges.

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#4 2010-07-30 19:47:47

DrPhil
Member
Registered: 2010-07-30
Posts: 4

Re: [SOLVED]What is fastest? MOD_AUTOLOAD="yes" or MOD_AUTOLOAD="no"

Thank you very much!
Now I have some more fun to read, and I got a good explanation!
I'll mark the thread as solved. smile

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#5 2010-07-30 20:03:45

falconindy
Developer
From: New York, USA
Registered: 2009-10-22
Posts: 4,111
Website

Re: [SOLVED]What is fastest? MOD_AUTOLOAD="yes" or MOD_AUTOLOAD="no"

Answer to the bonus question: Yes and no. If you leave out jbd2, when modprobe loads ext4, jbd2 will be loaded as well. Omitting a module (semantic) has no guarantee that said module will be blacklisted (which is obeyed by udev).

edit: removed nitpicking.

Last edited by falconindy (2010-07-30 20:27:19)

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