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Re: Paralell startup

Subject: Re: Paralell startup
From: Michael Wiktowy
Date: Wed, 20 Oct 2004 14:09:10 -0400

Date: Wed, 20 Oct 2004 10:53:17 -0400
From: Arjan van de Ven <arjanv@xxxxxxxxxx>
Subject: Re: Paralell startup

On Tue, 2004-10-19 at 12:10, Kyrre Ness Sjobak wrote:
I am hearing much good from the gentoo camp about paralell startup, and
how it brings down boot times to about 30 secounds. Is this possible to
do with fedora as well?
problem with parallel startup is that it *ALSO* increases how much the disk has to seek, which slows things down. For me it's not clear if it's actually a real gain or just a placebo one.


You are right ... just starting up everything that can possibly be started up all at once makes no sense since it will undoubtedly add overhead above and beyond the time for each to start separately.

There are some situations/landmarks that are independant of disk access though.
I would break things up into three phases of booting:
1) Hardware detection and configuration - pretty much everything has to wait for this (and all the HAL/hotplug/udev stuff is looking really slick, BTW) 2) Network connection - there are going to be many things that need to wait for a network interface to be established but many others that couldn't care less and could continue on loading up without waiting for slow DHCP resolution or a bit long timeout before ifup failure (both things catch me on a regular basis). 3) X server startup and presentation of GUI login - this could be spawned quite early on while everything else keeps loading in the background. Psychologically, many people believe that the boot is done when they can interact with the machine. Windows uses this trick extensively. While it looks like it has booted, try opening up an app ... it takes *ages* until it has truly finished loading everything in the background.

Each of these milestones can "fork" off a parallel ordered branch of startup scripts which may _seem_ to start up faster and avoid big pauses when there is trouble. It shouldn't add too much complication to the init. Each script just has to identify whether it needs networking to be up or if it blocks X.

/Mike

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