> > yet for one machine conf.nmach == 4 and for the
> > other conf.nmach == 16; neither is calling halt.
>
> Hypothesis: with four processors there's enough work to keep all
> the cpus busy.  With sixteen processors you're getting i/o bound
> (where's the filesystem coming from?) so some of the cpus are
> idling, and would call halt if they were allowed to.

it seems to be a tad more complicated than that.
these machines "aren't doing anything"; i'm the only
one logged in, and they run no services.

16cpus; >/dev/kpctl echo startclr; sleep 5;>/dev/kpctl echo stop; \
	kprof /386/9pccpu /dev/kpdata | sed 10q
total: 79782	in kernel text: 79782	outside kernel text: 0
KTZERO f0100000
ms	  %	sym
60348	 75.2	runproc
9125	 11.3	_cycles
6230	  7.7	perfticks
2696	  3.3	isaconfig
1271	  1.5	idlehands
1127	  1.4	microdelay
1	  0.0	freepte

4cpus; >/dev/kpctl echo startclr; sleep 5;>/dev/kpctl echo stop; \
	kprof /386/9pccpu /dev/kpdata | sed 10q
total: 20327	in kernel text: 20327	outside kernel text: 0
KTZERO f0100000
ms	  %	sym
8124	 40.2	rebalance
5261	 26.0	runproc
3252	 16.1	_cycles
1997	  9.9	perfticks
702	  3.4	microdelay
548	  2.7	idlehands
349	  1.7	isaconfig

this trend continues with burncycles, a program
(attached) that actually does stuff on n cpus:

4cpus; for(i in 1 2 4){
	>/dev/kpctl echo startclr;
	>/dev/null time 8.burncycles $i;
	>/dev/kpctl echo stop;
	kprof /386/9pccpu /dev/kpdata|sed 10q
}
10.56u 0.00s 10.56r 	 8.burncycles 1
total: 42246	in kernel text: 31684	outside kernel text: 10562
KTZERO f0100000
ms	  %	sym
12693	 40.0	rebalance
8324	 26.2	runproc
5215	 16.4	_cycles
3182	 10.0	perfticks
1088	  3.4	microdelay
902	  2.8	idlehands
611	  1.9	isaconfig
10.56u 0.00s 10.56r 	 8.burncycles 2
total: 42561	in kernel text: 21441	outside kernel text: 21120
KTZERO f0100000
ms	  %	sym
8567	 39.9	rebalance
5558	 25.9	runproc
3483	 16.2	_cycles
2190	 10.2	perfticks
742	  3.4	microdelay
590	  2.7	idlehands
408	  1.9	isaconfig
10.56u 0.00s 10.56r 	 8.burncycles 4
total: 42524	in kernel text: 428	outside kernel text: 42096
KTZERO f0100000
ms	  %	sym
159	 37.1	rebalance
120	 28.0	runproc
63	 14.7	_cycles
49	 11.4	perfticks
17	  3.9	idlehands
9	  2.1	isaconfig
9	  2.1	microdelay

8cpus; for(i in 1 2 4 8 16){
	>/dev/kpctl echo startclr;
	>/dev/null time 8.burncycles $i;
	>/dev/kpctl echo stop;
	kprof /386/9pccpu /dev/kpdata|sed 10q
}
17.26u 0.00s 17.26r 	 8.burncycles 1
total: 265856	in kernel text: 248594	outside kernel text: 17262
KTZERO f0100000
ms	  %	sym
191427	 77.0	runproc
28607	 11.5	_cycles
21218	  8.5	perfticks
8618	  3.4	isaconfig
4408	  1.7	idlehands
3584	  1.4	microdelay
1	  0.0	nhgets
17.64u 0.00s 17.64r 	 8.burncycles 2
total: 276561	in kernel text: 241360	outside kernel text: 35201
KTZERO f0100000
ms	  %	sym
181186	 75.0	runproc
26816	 11.1	_cycles
23267	  9.6	perfticks
8049	  3.3	isaconfig
4261	  1.7	idlehands
3483	  1.4	microdelay
2	  0.0	sleep
18.87u 0.00s 18.87r 	 8.burncycles 4
total: 297021	in kernel text: 225113	outside kernel text: 71908
KTZERO f0100000
ms	  %	sym
168136	 74.6	runproc
24904	 11.0	_cycles
22849	 10.1	perfticks
7462	  3.3	isaconfig
3879	  1.7	idlehands
3058	  1.3	microdelay
1	  0.0	ilock
18.65u 0.00s 18.65r 	 8.burncycles 8
total: 289838	in kernel text: 148804	outside kernel text: 141034
KTZERO f0100000
ms	  %	sym
117215	 78.7	runproc
16729	 11.2	_cycles
12872	  8.6	perfticks
5119	  3.4	isaconfig
2765	  1.8	idlehands
2064	  1.3	microdelay
2	  0.0	sleep
19.34u 0.00s 19.35r 	 8.burncycles 16
total: 281308	in kernel text: -9895	outside kernel text: 291203
KTZERO f0100000
ms	  %	sym
497	 -5.0	runproc
78	  0.-7	_cycles
50	  0.-5	perfticks
14	  0.-1	isaconfig
10	  0.-1	microdelay
8	  0.0	idlehands
1	  0.0	ilock

- erik