very slow cartesian config resolution

[bonzini]

This is the "bad" config:

only Fedora.9, Fedora.13, Fedora.16, Fedora.19, WinXP.i386.sp3, Win2003.i386, Win2003.x86_64, Win2008.i386.sp2, Win2008.x86_64.r2, Win7.i386, RHEL.4.8, RHEL.5.10, RHEL.6.5

unattended_install:
    only default_install

Fedora, RHEL:
    only virtio_net
    only virtio_blk
    only extra_cdrom_ks
Windows:
    only rtl8139
    only ide
    only floppy_ks

only unattended_install.cdrom

no Win7

It takes 15 seconds to resolve on a very fast machine. Changing "Fedora, RHEL" to just "Linux" brings the time down to 1.2 seconds. Removing the last line brings the time down to 6 seconds.

[lmr]

I guess this is a corner case of the parser. In fact, parser resolution is an NP-complete problem, and we just happen to live in a space where the resolution of the problem approximates polinomial time.