ThinClientFasterStartup

Revision 14 as of 2005-11-05 17:44:43

Clear message

Summary

Speed up the Thin Client bootprocess for LTSP

Rationale

Ubuntu 5.10 thin clients take ages to boot. Some of the generic startup time improvements will also apply to thin clients, but we should specifically optimize the thin client startup process as well. Thin clients are usually low-spec hardware and need this more than most.

Use cases

Matthew gives a class on usability at university where he uses LTSP in his class, if he's the first in the class for the day he expects his pupils to be able to work immediately after switching on the Thin clients.

Scope

The boot process of LTSP Thin Clients as well as the default bootstrapping of the thin client chroot environment.

Design

  • Rip out the unneeded services from Thin Clients
  • Fix the delay of nfs mounting in klibc

ScottJamesRemnant: do you have any idea why this happens? If so, please document it here for other people -- if not please explicitly say you need to investigate it rather than just fix it.

  • Compare the list of started services between LTSP 4.1 and breezy LTSP
  • Remove the "sleep 3" from the initramfs nfs script

ScottJamesRemnant: this sleep is usually needed, it's not just there for fun. Please indicate that you have researched why this is there, and that it is safe to remove.

  • start LDM as early as possible in the bootprocess

ScottJamesRemnant: please document its dependencies, so somebody else can evaluate how early it can be.

  • find the slowing down part in syslogd (strace) and fix it

ScottJamesRemnant: do you have any idea why this happens? If so, please document it here for other people -- if not please explicitly say it needs to be investigated.

  • run a ntpd on the ltsp server and make the thin client pull its time from there

MattZimmerman: better to disable ntpdate at boot unless the user explicitly configures an NTP server in lts.conf, rather than adding a new default service to the server. Most installations probably don't care if the clock on the thin clients is accurate.

  • make ltsp-build-client's debootstrapping install only the bare minimum needed (probably introduce a thin client mode)
  • drop module-init-tools from the bootprocess

ScottJamesRemnant: err... depmod and udev kinda need that

  • find any silent scripts that run and might slow down the bootprocess

Implementation

Cutting down the list of started services in rcS.d on the Thin Client to the following gains us 30 seconds:

  • S02mountvirtfs
  • S04udev

ScottJamesRemnant: both being moved to initramfs and being replaced with a "catchup"

  • S32ltsp-client-setup
  • S40hotplug

ScottJamesRemnant: being removed, replaced by initial boot

  • S40networking

ScottJamesRemnant: do you want this, or Network Manager on the clients?

  • S50alsa-utils
  • S70xorg-common

This seems to be the bare minimum of bootscripts. The boot process still needs ~60 seconds from hitting the power button (which includes BIOS indeed) to being able to log in at the login manager (which is about as much as a normal ubuntu workstation installation), mostly caused by initramfs and hotplug which should be sped up by changes Scott will make to the initramfs/hotplug architecture.

MattZimmerman: doesn't describe how these changes will be implemented (omitting packages via debootstrap, removing symlinks in ltsp-client-setup, a mixture of the two?

Code

Changes in ltsp-build-client are required to remove the unneeded startup scripts. The initramfs and hotplug changes are covered in other specs. The ltsp-client startscript should move up to the top of rc2.d Giving readahead-list a list of files to preload on boot.

MattZimmerman: readahead is tricky, since it may hurt more than it helps if the client hasn't much memory. I suggest this not be part of the initial implementation, and that careful measurements be made before enabling it by default. We can consider it as a future optimization, perhaps an optional one enabled in lts.conf.

Data preservation and migration

Breezy users will either need to rebuild their chroot environment (recommended, since the initramfs/hotplug changes will yield the most speedup), or we could provide a script that disables the unneeded services.

Outstanding issues during development

Examine the initramfs/hotplug speedup that can be done.

Examine the gain of the inclusion of readahead-list in the bootprocess.

Examining debootstrap for things that dont need to be installed (having a ltsp mode for debootstrap)