filemon: weird full-time build although filemon enabled

I build CURRENT on two technically similar systems on a almost daily basis. Therefore, it
was a great relief having WITH_META_MODE=yes set in /etc/src-env.conf for incremental
builds. To make my understanding of this clear (just in case I'm wrong): setting
WITH_META_MODE builds only portions that does not need to be build in the make context.

Well, the reason writing this email is: on one system, I run almost every reboot into a
"full build" and this puzzles me a bit. The long-lasting and time exhausting builds are
within the LLVM/CLANG tree. They consume a lot of time. The box in question does have a
weak CPU, only two physical cores, four threads, 8GB of RAM and builds the /usr/obj
residing on a SSD. The reference machine does have the same motherboard, also a SSD, but
has 16 GB RAM and a 4-core/8 threads XEON CPU - but both are "IvyBridge". The XEON
usually needs 30 - 40 minutes to compile a full world/kernel from a clean /usr/obj, the
"weak" box takes approximately 120 minutes - it is understandable that a shortage of the
build time is appreciated.

Well, having said this, I need to mention that both systems use almost
identical /etc/src.conf setting - except the order of appearance of the WITH_ tags. In
fact, they are identical except the KERNCONF (naming of the kernel) and PORTS_MODULES=,
the "weak" box incorporates x11/nvidia-driver and emulators/virtualbox-ose-kmod, so these
modules are build every time the system gets rebuild, but the time taken by those is
negligible.

The problem: to make my point clear: the "weak" box starts compiling almost everytime now
the LLVM/CLANG tree while the XEON box does not. This is spooky.

I deleted on both  systems recently /usr/obj completely from its content and restarted a
buildworld again to hope, that the problem was introduced due to some files
necessary for the BSD make environment to indicate the incremental build. But no success.
Even more spooky is the fact, that after a build on the "weak" box and a build again, the
box bevaves as expected not rebuilding everything again, but in some cases after a
reboot, a rebuild the hits again the build of LLVM/CLANG tree, while the XEON box does
not.

I think there is something missing an I'd like to ask what is the suggested way to
initially restart a full build to ensure that WITH_META_MODE gets initialised correctly.

Well, I'm not a developer, so please be patient with my naive report.

Thanks in advance,

oh

-- 
O. Hartmann

Ich widerspreche der Nutzung oder Übermittlung meiner Daten für
Werbezwecke oder für die Markt- oder Meinungsforschung (§ 28 Abs. 4 BDSG).