On Monday, 12 February 2001 at 15:29:17 +0100, Dag-Erling Smorgrav wrote:
> Danny Braniss <[EMAIL PROTECTED]> writes:
>> i've been doing some experiments with vinum, and doing a make buildworld
>> (with obj on the same vinum)
>> without soft-updates ~ 1 hour
>> with soft-updates ~ 40 minutes
>> which is a bit better than 3% :-)
>>
>> what i can't figure out is why -j 4 didn't make any difference.
>
> Because your I/O system is already saturated. The point with -jNN is
> that one job can run while another is waiting for I/O to complete and
> vice versa, but as your CPU gets faster the time spent actually
> compiling etc. becomes insignificant next to the time spent doing I/O,
> and if you're already doing I/O as fast as you can there's no room for
> improvement. On a machine with a slower CPU or a faster I/O system,
> you'd see improvement.
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.
Greg
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