* Greg Lehey <[EMAIL PROTECTED]> [010212 15:23] wrote:
> 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.
Actually compiles are pretty meta-data intensive, almost compiled
program is composed of several .o files, without softupdates those
.o files are expensive to create. Another thing is temp files for
preprocessor output and assembler output, these can be reduced by
using -pipe but without -pipe, each compile takes probably 3 file
creations, 3 sync ops without softupdates. So basically, using
softupdates along with -jN make actually does make a difference.
--
-Alfred Perlstein - [[EMAIL PROTECTED]|[EMAIL PROTECTED]]
"I have the heart of a child; I keep it in a jar on my desk."
To Unsubscribe: send mail to [EMAIL PROTECTED]
with "unsubscribe freebsd-hackers" in the body of the message
