calcru: negative time (Interrupt Storm on cpu0: timer)

[Frank Steinborn]

Hello,

After reboot yesterday, my system suddenly started to flood syslog with
following message:

calcru: runtime went backwards from 1966191374 usec to 1966189453 usec
for pid 29988 (screen)

It's not only screen, i saw sh and su also, but in the last hour only
screen. A vmstat -i and the same 5 seconds later:

interrupt                          total       rate
irq1: atkbd0                           1          0
irq13: npx0                            1          0
irq14: ata0                       410366          5
irq17: em0                      20882069        263
cpu0: timer                    158483081       2000
Total                          179775518       2268

interrupt                          total       rate
irq1: atkbd0                           1          0
irq13: npx0                            1          0
irq14: ata0                       410430          5
irq17: em0                      20885602        263
cpu0: timer                    158505514       2000
Total                          179801548       2268

Is this an interrupt storm? I know that there is a FAQ entry about the
negative time issue, but it seems this is more a bad workaround I 
guess. The system was running without problems for 3 months or so and
as I said the problem suddenly appeared yesterday.

Any hints on whats wrong here?

Thanks in advance,
Frank