> In fact, it's exactly the opposite. 'make world' is CPU-bound, so the
> speed of the I/O system is irrelevant. If it were I/O bound, soft
> updates *would* make a difference, because a number of unnecessary
> writes would be eliminated.
Actually, I have measured that after a certain point make world *is*
I/O bound and you can't really get any faster unless you do something
to the I/O subsystem. We have several quad Xeons here, and back when
I was more interested in measuring this sort of thing I found that I
could get a "worldstone" time of around 37 minutes with -j8 and all 4
processors churning away. This was also during the exclusively BGL
days of -current and things may scale slightly better or worse now, I
dunno, but what I did find was that I could drop this all to something
more like 23 minutes simply by putting /usr/src and /usr/obj into MFS
(the machine I used also has a gigabyte of memory so this isn't
difficult to do). That implies to me, at least, that after a certain
point the CPU is going to be the bottleneck.
- Jordan
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