void wrote:
>
> On Mon, Feb 12, 2001 at 10:36:40PM -0800, Jordan Hubbard wrote:
> >
> > With how many running processors? If you're running -j4 on a
> > uniprocessor system, you're only introducing competition for already
> > scarce CPU resources, though -j2 can be a speedup since this allows
> > one target build to run while another is in an I/O wait. I've only
> > seen a speedup with -j4 when using at least 2 CPUs.
>
> Interesting. When I asked about optimal values on this list maybe a
> year ago, I was told that -j(4 * NCPU) was a good choice. I guess that
> doesn't work for NCPU == 1.
I did some testing last night and found that there was a difference of
50% between -j4 and not running softupdates and running softupdates
and no -j4. The buildworld elapsed clock times were 58 minutes for the
first case and 38 minutes for the last case. Even -j2 added 11 minutes
to the elapsed build time. I thought I had been hit by one of the file
system cron jobs on -j2 and ran it again. The difference was around 10
seconds between the two runs. The user time isn't that much different
but the -jn contention really slows the buildworld down.
The times are in a table at
http://dsl1-160.dynacom.net/freebsd/urban_legends.html
kent
>
> --
> Ben
>
> "I told Paddy no, I told Steve no, I told Paul no, and Ben fell asleep."
> --Kate C. (no, different Ben, I would have stayed up)
--
Kent Stewart
Richland, WA
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