Re: CD sizes again (and BoF reminder!)

[Simon Paillard <spaillard@debian.org>]

Hi,

On Sat, Jul 21, 2012 at 09:25:50PM +0300, Uoti Urpala wrote:
> Joey Hess wrote:
> > Hideki Yamane wrote:
> > >  I tested as well, and sometimes decompression with xz is so sloooow,
> > >  it takes 6-8 times than default gz.
> > 
> > I was just watching your DebConf presentation "Lets shrink Debian
> > package archive" and I think there you said decompression with xz was
> > between 2x and 6x slower. Is that the current number?
> > 
> > I'm concerned with the thought that installation of Debian (as well
> > as debootstrap) could take twice or more as long if xz were used for
> > say, every package on a Gnome desktop CD. In d-i we try to make
> > installation faster; slow installs make people less happy. It would
> > be useful to have some real-world installation time benchmarks with
> > and without xz.
> 
> Does unpacking really take a substantial portion of the time used by the
> installer? 
[..]
> So at least in this case the biggest performance problem by far is the
> inappropriate use of fsync() or other disk synchronization primitives,
> and CPU use for unpacking is pretty much irrelevant.

Though the kernel will have to sync sooner or later, I understand
debian-installer ask dpkg not to fsync:

http://bugs.debian.org/605384
 base-installer (1.121) unstable; urgency=low
 .
   [ Colin Watson ]
   * Merge from Ubuntu:
     - Run dpkg with --force-unsafe-io during installation; syncing is
       unnecessary in this context and can slow things down quite a bit
       (closes: #605384).

-- 
Simon Paillard