[Proof of Concept] Stacked unionfs based 'tinderbox'

[Ulrich Spörlein]

On Thu, 25.02.2010 at 10:08:15 +0200, David Naylor wrote:
> Hi,
> 
> As some may have noticed on -current I have been working on using
> stacked unionfs to implement a 'tinderbox' type build system.  I have
> successfully used the scripts to build x11/xorg (and have compared the
> results to using the traditional approach using pkg_add).  The build
> system is stable except for one nasty corner case: deadlocks.

When I did this a couple of years ago, the major problems were failing
chdir(2) calls during ports build, etc.

> To setup a compatible test environment requires:
>  - recompile the kernel with `options KSTACK_PAGES=32`, otherwise the
>  kernel will panic with a double fault.  WITNESS options results in
>  substantial performance degradation.
>  - patch mtree (see below) [optional]
>  - create the appropriate chroot environment (and reboot) [see below
>  for corner case]
> 
> A performance bottleneck in mtree was identified.  This resulted in
> mtree (as run by port install) consuming ~20% of the build time.  See
> bin/143732 for a patch and further details.

Good work!

> The normal tinderbox approach takes ~80% more time to install compared to the
> quick and dirty approach.  The stacked unionfs approach takes ~170% more time
> (an increase of ~50% over the tinderbox approach).  Some performance gains can
> be had if one uses memory backed storage (vs HDD in this case).

Please explain: what is the quick and dirty approach and which one is
faster now?

As your scripts did not make it through, perhaps you can upload them to
the wiki? What I did back then was using a clean base system as the
underlying unionfs store to avoid re-generating the clean base over and
over again. Nowadays, a ZFS clone would probably be the way to go.

I'm not sure if a recursive approach is feasible here, as you can have
only one underlying unionfs mount. But special casing, e.g., perl may
still give a massive speedup. So for each port that has perl as
dependancy, you would not pull in the clean base + pkg_add perl, but
instead grab the clean-base+perl directory as an underlying unionfs.

Cheers
Uli