[Bug 2065180] Re: performance regression in dracut-install

[Dave Jones]

Some results from some local testing. These tests were all performed on
the same SD card (a Samsung EVO Select 64GB) with fresh installs of the
jammy and noble server images, after running full upgrades and
rebooting:

Pi 5,   noble -- 01:23
Pi 4B,  noble -- 03:05
Pi 3B+, noble -- 05:19

Pi 5,   jammy -- unsupported
Pi 4B,  jammy -- 01:06
Pi 3B+, jammy -- 01:59

So, there *appears* to be a substantial slow down from jammy. However, I
don't think this is due to dracut or a performance regression in
initramfs-tools. I remembered that, this cycle, the kernel team got rid
of the linux-modules-extra split in the linux-raspi kernel. This results
in a substantially increased initrd size because many more modules are
included by default.

I took a listing of the jammy and noble initramfs contents and (after
some manipulation to remove .zst suffixes, which are also new in the
noble initramfs, and removing kernel version numbers). I'll attach the
result of diff'ing these outputs, but a quick grep through the results
and some calculations shows roughly 1000 extra files in the noble
version.

In other words, this is not comparing like for like.

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https://bugs.launchpad.net/bugs/2065180

Title:
  performance regression in dracut-install

Status in dracut package in Ubuntu:
  New

Bug description:
  When compared to Ubuntu 23.10, creating intramfs files with update-
  initramfs takes 2 to 5 times more time on ARM devices.

  IIUC, dracut-install usage was added to initramfs-tools to speed up
  the process. But now its way slower. Even running update-initramfs on
  jammy, which doesn't use dracut-install, is way faster then the time
  taken on Noble.

  first bad commit -
  https://github.com/dracutdevs/dracut/commit/3de4c7313260fb600507c9b87f780390b874c870

  $ lsb_release -rd
  No LSB modules are available.
  Description:	Ubuntu 24.04 LTS
  Release:	24.04

  $ apt-cache policy dracut-install
  dracut-install:
    Installed: 060+5-1ubuntu3
    Candidate: 060+5-1ubuntu3
    Version table:
   *** 060+5-1ubuntu3 500
          500 http://ports.ubuntu.com/ubuntu-ports noble/main arm64 Packages
          100 /var/lib/dpkg/status

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