Fujitsu lifebook A544, after bios update, kacpid using processor

[Colin Law]

I booted into Windows on my Fujitsu Lifebook A544 and was notified
that there was an important BIOS upgrade which would make it less
likely that my battery would self ignite, so I upgraded it to the
latest (1.25).  Now, however, in Ubuntu, the system monitor shows that
something is permanently using about 60% of one of the cores, but the
process list shows nothing using anything like that amount of
processor.
Using htop and hitting K, which I think then shows kernel threads, it
appears to show that the culprits are kworkers kacpid, kacpi_notify.
Googling suggests that others with similar problems have solved it by
various means including installing acpi (no difference) and adding
kernel parameter noapic (which made it worse).  Has anyone any other
ideas which might help?

Colin