amd64/152405: wrong user time is reported when CPU frequency throttled.

[KOIE Hidetaka]

>Number:         152405
>Category:       amd64
>Synopsis:       wrong user time is reported when CPU frequency throttled.
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Nov 19 12:40:06 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     KOIE Hidetaka
>Release:        9.0-CURRENT
>Organization:
surigiken
>Environment:
FreeBSD guriandgura 9.0-CURRENT FreeBSD 9.0-CURRENT #0: Wed Nov 17 15:11:51 JST 2010     root at guriandgura:/usr/obj/museum/freebsd/sys/GURIANDGURA  amd64

SVN revision is 215415.
>Description:
when CPU frequency is throttled down, time command reports too low CPU usage like this:
4.849u 0.000s 0:09.13 53.0%     9+5026k 0+0io 0pf+0w
100% is expected, because the process is extreamly CPU-intensive.

wall clock is precise.

systat -vm 1 shows collect user time (25% in 4-core system).

>How-To-Repeat:
koie at guriandgura% cat loop.c
int
main()
{
    unsigned long x = 0xffffffffUL;
    printf("%lx\n", x);
    while (--x > 0)
        ;
    return 0;
}
koie at guriandgura% gcc46 -O loop.c -o loop
loop.c: In function 'main':
loop.c:5:5: warning: incompatible implicit declaration of built-in function 'printf' [enabled by default]

>Fix:
I don't know.

>Release-Note:
>Audit-Trail:
>Unformatted:
 >>>sysctl dev.cpu.0.freq=1800
 
 koie at guriandgura% date ; time ./loop ; date
 Fri Nov 19 16:58:27 JST 2010
 ffffffff
 4.828u 0.000s 0:04.96 97.1%     5+2771k 0+0io 0pf+0w
 Fri Nov 19 16:58:32 JST 2010
 
 >>>sysctl dev.cpu.0.freq=1000
 
 koie at guriandgura% date ; time ./loop ; date
 Fri Nov 19 16:58:54 JST 2010
 ffffffff
 4.838u 0.008s 0:09.08 53.1%     9+5037k 0+0io 0pf+0w
 
 NOTE:
   53.1% / 97.1% = 0.546.
   1000 / 1800 = 0.555.
 
 NOTE:
 koie at guriandgura% sysctl kern.sched kern.eventtimer
 kern.sched.cpusetsize: 8
 kern.sched.preemption: 1
 kern.sched.topology_spec: <groups>
  <group level="1" cache-level="0">
   <cpu count="4" mask="0xf">0, 1, 2, 3</cpu>
   <children>
    <group level="2" cache-level="2">
     <cpu count="2" mask="0x3">0, 1</cpu>
    </group>
    <group level="2" cache-level="2">
     <cpu count="2" mask="0xc">2, 3</cpu>
    </group>
   </children>
  </group>
 </groups>
 
 kern.sched.steal_thresh: 2
 kern.sched.steal_idle: 1
 kern.sched.steal_htt: 1
 kern.sched.balance_interval: 127
 kern.sched.balance: 1
 kern.sched.affinity: 1
 kern.sched.idlespinthresh: 16
 kern.sched.idlespins: 10000
 kern.sched.static_boost: 160
 kern.sched.preempt_thresh: 64
 kern.sched.interact: 30
 kern.sched.slice: 12
 kern.sched.name: ULE
 kern.eventtimer.choice: LAPIC(400) i8254(100) RTC(0)
 kern.eventtimer.et.LAPIC.flags: 15
 kern.eventtimer.et.LAPIC.frequency: 100006412
 kern.eventtimer.et.LAPIC.quality: 400
 kern.eventtimer.et.i8254.flags: 1
 kern.eventtimer.et.i8254.frequency: 1193182
 kern.eventtimer.et.i8254.quality: 100
 kern.eventtimer.et.RTC.flags: 17
 kern.eventtimer.et.RTC.frequency: 32768
 kern.eventtimer.et.RTC.quality: 0
 kern.eventtimer.periodic: 0
 kern.eventtimer.timer: LAPIC
 kern.eventtimer.idletick: 0
 kern.eventtimer.singlemul: 2
 koie at guriandgura%