[Bug 947664] Re: Unpacking linux-headers unbelievably slow in Lubuntu Precise (Beta 1)

[Raphaël Hertzog]

On Wed, 30 May 2012, Brian J. Murrell wrote:
> Over the same NFS with --force-unsafe-io it takes 26 minutes and that's
> probably because in analysing with strace, I don't see dpkg doing
> anything different per file being installed:

That's because the fsync() are done in a batch at the end of the
unpacking. So the per-file operations at the start are the same...
but when you use --force-unsafe-io you don't have the serie of fsync()
at the end.

> read(9, "/*\n * Generic GPIO API implement"..., 1196) = 1196
> write(10, "/*\n * Generic GPIO API implement"..., 1196) = 1196
> read(9, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 340) = 340
> sync_file_range(0xa, 0, 0, 0)           = 0


> So it seems there is still a sync being done after each file is written,
> even with --force-unsafe-io.

sync_file_range() is something different, it just tells the filesystem to
start the writeback, it doesn't wait for it to have happened (contrary to
fsync()).

So it should be irrelevant for the time lost, unless Linux's NFS driver
has a poor handling of this Linux-specific function.

Cheers,
-- 
Raphaël Hertzog ◈ Debian Developer

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https://bugs.launchpad.net/bugs/947664

Title:
  Unpacking linux-headers unbelievably slow in Lubuntu Precise (Beta 1)

Status in “dpkg” package in Ubuntu:
  Incomplete

Bug description:
  The below is an example line in an apt-get dist-upgrade which seems to
  take 30 minutes or more on a 2.1GHz CPU (one core of a quad core
  through Virtualbox). I've been looking at it for ages, and even had
  time to log in here and file the bug  - the line is still 'hung'.

  Unpacking linux-headers-3.2.0-18 (from .../linux-
  headers-3.2.0-18_3.2.0-18.28_all.deb)

  Can anyone explain this, or is it a bug in the configuration of
  Lubuntu, Apt-get or something. I read that there was a similarly
  behaving bug to do with dpkg using paranoid file synchronization but
  this length of delay is frankly a bit crazy.

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