[Bug 1965129] [NEW] flash-kernel is extremely slow on raspi

[Dave Jones]

Public bug reported:

Currently flash-kernel takes at least 1 and a half minutes (on fast SSD
storage) to execute on a Raspberry Pi. This is partly because a
considerable number of files are transferred compared to other platforms
(all supported dtbs, and their overlays, along with the kernel and
initrd which totals several hundred copy operations in all). However, a
large part of this is that "maybe_defrag" is called at the end of
"backup_and_install".

The "maybe_defrag" function checks the f-k database for the "Bootloader-
Has-Broken-Ext4-Extent-Support" flag to determine whether a
defragmentation run is required (it's not on Pi models). Unfortunately,
it checks this *every time* and the check is fairly expensive (involves
bash parsing the f-k database). If this value is cached (as many other
values from the database are), this reduces the overall f-k runtime to
~22 seconds (again, on fast SSD storage).

** Affects: flash-kernel (Ubuntu)
     Importance: Undecided
     Assignee: Dave Jones (waveform)
         Status: New

** Changed in: flash-kernel (Ubuntu)
     Assignee: (unassigned) => Dave Jones (waveform)

** Changed in: flash-kernel (Ubuntu)
    Milestone: None => ubuntu-22.04

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https://bugs.launchpad.net/bugs/1965129

Title:
  flash-kernel is extremely slow on raspi

Status in flash-kernel package in Ubuntu:
  New

Bug description:
  Currently flash-kernel takes at least 1 and a half minutes (on fast
  SSD storage) to execute on a Raspberry Pi. This is partly because a
  considerable number of files are transferred compared to other
  platforms (all supported dtbs, and their overlays, along with the
  kernel and initrd which totals several hundred copy operations in
  all). However, a large part of this is that "maybe_defrag" is called
  at the end of "backup_and_install".

  The "maybe_defrag" function checks the f-k database for the
  "Bootloader-Has-Broken-Ext4-Extent-Support" flag to determine whether
  a defragmentation run is required (it's not on Pi models).
  Unfortunately, it checks this *every time* and the check is fairly
  expensive (involves bash parsing the f-k database). If this value is
  cached (as many other values from the database are), this reduces the
  overall f-k runtime to ~22 seconds (again, on fast SSD storage).

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