device driver / char module interrupt vector -> user space code

[SA]

Dear Kernel List,

I am writing a char module for a PCI stage controller and want to add the 
following functionality; 

The device will generate an interrupt (or software trigger) and I want this to 
run a bit of user code with relatively latency.  (<1ms).  I am unclear how to
do this while still separating the user from the kernel code and maintaining
security - would this usually be handled by issuing a signal to the user space
process? if so how and what latency can I expect? 

Thanks matt

(more info: the stage controller moves little mechanical platforms in an 
experiment, as the platforms reach certain positions (determined by
the hardware or the driver) user code must be run to perform some
action (say take a measurement).  The stages move continuously so
timing errors map to positional errors.  I could do all this in kernel space
by linking the various drivers controlling the various hardware together
under a super-driver for the entire experiment, however, it would be
much nicer to achieve this with separate modules and user code).