ksoftirqd is a per-cpu kernel thread that runs when the machine is under heavy
soft-interrupt load. Soft interrupts are normally serviced on return from
a hard interrupt, but its possible for soft interrupts to be triggered
more quickly than they can be serviced. If a soft interrupt is triggered
for a second time while soft interrupts are being handled, the
ksoftirq daemon is triggered to handle the soft interrupts in process context.
ksoftirqd is taking more than a tiny percentage of CPU time, this indicates the
machine is under heavy soft interrupt load.