[Bug 203284] arm64: bogus CPU % accounting in top

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203284

            Bug ID: 203284
           Summary: arm64: bogus CPU % accounting in top
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: arm64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: emaste at freebsd.org

a.out is a CPU-bound process that spins at 100% reading and writing memory in a
loop, with 32 copies running in parallel on the 48-core system, so I'd expect
to see all of them reporting 100% CPU.

A snapshot of top looks like:

  PID USERNAME    THR PRI NICE   SIZE    RES STATE   C   TIME    WCPU COMMAND
  822 root          1 103    0  1030M  1024M CPU2    2  34:38 1779.83% a.out
  819 root          1 103    0  1030M  1026M CPU17  17  34:41 458.17% a.out
  817 root          1 103    0  1030M  1026M CPU44  44  34:41 444.14% a.out
  815 root          1 103    0  1030M  1026M CPU42  42  34:41 444.14% a.out
  806 root          1 103    0  1030M  1012M CPU38  38  34:44 356.67% a.out
  807 root          1 103    0  1030M  1013M CPU30  30  34:44 356.24% a.out
  812 root          1 103    0  1030M  1021M CPU5    5  34:41  31.81% a.out
  837 root          1  20    0  7660K  1896K CPU25  25   3:16   1.63% top
  809 root          1 103    0  1030M  1020M CPU32  32  34:41   0.00% a.out
  814 root          1 103    0  1030M  1021M CPU26  26  34:40   0.00% a.out
  811 root          1 103    0  1030M  1020M CPU45  45  34:40   0.00% a.out
  810 root          1 103    0  1030M  1016M CPU24  24  34:40   0.00% a.out
  805 root          1 103    0  1030M   995M CPU29  29  34:38   0.00% a.out
  820 root          1 103    0  1030M  1016M CPU33  33  34:38   0.00% a.out
  821 root          1 103    0  1030M  1020M CPU8    8  34:37   0.00% a.out
  818 root          1 103    0  1030M  1005M CPU19  19  34:37   0.00% a.out
  808 root          1 103    0  1030M  1005M CPU36  36  34:36   0.00% a.out

Sometimes many process report 400% or so, sometimes only a few.

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