Comparing buildworld times on twin machines

[Mark Terribile]

Charles Howse writes:

> I have 2 machines on my home network with (almost)
> identical hardware.  ... The only difference is
> that curly has 128 MB ram where larry has only 64.

Memory available for caching certainly can make a
difference.  Remember that FreeBSD uses ALL otherwise
uncommitted memory for caching, and so a machine with
more memory may do less disk I/O.

> They *do not*, however have identical hard drives,
> even though each machine has 2 drives, with
> /usr/obj on the second drive of each machine.

And building things can do a lot of disk I/O, and
a lot of directory lookups, especially if you have
recursive make(1) operations.

> Larry can buildworld in 1 hr 57 mins.  It takes
> curly 3 hrs 16 mins, even though curly has twice
> the ram.

> If I watch the compile, with one eye on the disk
> activity light, it seems to me that the process is
> largely CPU intensive, therefore I would expect
> that the buildworld times should be roughly equal.

Instead of watching just the disk lights, start up
 systat 1 -vmstat  in a free window or console.
Learn what the various indicators mean.  You'll
probably be able to find your answers there.
systat(8) is really an incredible tool for
understanding where the system is spending its time,
and how.


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