i386/43491: microuptime () went backwards

[Simon Walton]

> 
> Just to add to the record, I have seen this to also be part
> of the effects of a broken SCSI drive, apparently with the drive's
> electronics gone stale.  Sometimes just a massive stream of the
> above microuptime()... messages whenever the disk was accessed,
> and after some time (but not always) followed by a total lockup
> with a bus reset every second (but sometimes just thousands of
> microuptime() messages, system was going normal apart from that,
> except for time+date and the logfile filling, of course.)
> Removing the drive fixed that.

   I've noticed that the errors sometimes correspond to
heavy disk use (on either of its two disks), but I am
not seeing bus resets and the disks otherwise seem fine.

   I can clear the condition by setting the i8254 frequency
with sysctl -w machdep.i8254_freq, even if I don't actually
change the frequency. I've also noticed this message on 
startup

APIC_IO: MP table broken: 8259->APIC entry missing!

so I suspect my problem is related to APIC interrupts.

Simon