Re: CD sizes again (and BoF reminder!)
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? In my experience the installer takes a LOT longer than it
would take to unzip a CDs worth of data.
Most of the time taken by cdebootstrap is wasted by dpkg on doing
useless file syncs:
cdebootstrap --arch=amd64 unstable debian-tree/
from local package cache on ext4: 138 seconds
on tmpfs where dpkg can't waste time on useless syncs: 21 seconds (and a
significant portion of that is used by package scripts with "sleep 1")
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.