compile: why not max-out resources?

[Beeblebrox]

I have two questions re compiling vs CPU + HDD throughput. CPU is Athlon-II,
HDD is sata-3 + ZFS

1. When compiling world and some ports, neither CPU usage, nor HDD
throughput (from gstat) is maximized (threads are defined in make.conf) and
in many instances usage is very low. Is there a third parameter limiting the
speed of the first two?
2. I have noticed that when compiling world resource usage fluctuates
greatly, but that 10 and 11 both take considerably longer compared to 9 and
that ccache is ineffective. Is this normal?
PS. buildworld for both 10 and 11 halted at libiconv phase when ccache was
enabled in make.conf. Proceeded without ccache.



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FreeBSD-9.2-stable_amd64_root-on-zfs_clang-only-world
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