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Date:      Sat, 23 Nov 1996 17:43:09 -0700
From:      Steve Passe <smp@csn.net>
To:        dg@Root.COM
Cc:        freebsd-smp@freefall.freebsd.org, Peter Wemm <peter@spinner.dialix.com>
Subject:   Re: SMP -current merge 
Message-ID:  <199611240043.RAA20563@clem.systemsix.com>
In-Reply-To: Your message of "Sat, 23 Nov 1996 15:23:25 PST." <199611232323.PAA02050@root.com> 

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Hi,

I have tested the times reported by "time make" against a stopwatch,
and they are accurate to within 0.5 second.  I was surprised to see
increasingly better times beyond "-j 2".  I guess this is from
parallelism on the disk accesses, ie when both CPUs are waiting for
disk IO on a particular object build, there is another they can work
on if jobs > 2.  The point of diminishing returns seems to be
around 8 jobs.

------------------------------
Summary of kernel build times:

---
1 CPU active, non SMP kernel:
# time make:		446.65s real  337.68s user   22.54s system

---
2 CPUs active, idlequeue search in smp_idleloop():
# time make:		597.45s real  373.91s user  147.68s system

---
2 CPUs active, NO idlequeue search in smp_idleloop():

# time make:		433.87s real  332.11s user   44.69s system
# time make -j 2:	326.28s real  400.29s user   67.71s system
# time make -j 3:	293.41s real  420.08s user   77.28s system
# time make -j 4:	285.10s real  425.32s user   79.71s system
# time make -j 5:	277.74s real  428.25s user   78.97s system
# time make -j 6:	276.35s real  429.64s user   80.22s system
# time make -j 7:	274.97s real  432.54s user   80.01s system 
# time make -j 8:	274.53s real  431.80s user   81.16s system
# time make -j 9:	276.46s real  433.53s user   81.20s system

--
Steve Passe	| powered by
smp@csn.net	|            FreeBSD

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