Excessive amount of time in interrupt stack mode

[Carlos E Murillo-Sanchez via cctalk]

Dear ccmp'ers:

For a while now, I noticed that my vaxstation 4000/60 with OpenVMS 7.2 
had become sluggish, but I had not had the time to investigate the 
problem.   The system is mostly idle, RAM is mostly free (there's 32mb), 
there is almost no paging, but the CPU is spending upwards of 70% of the 
time in the interrupt stack mode.  Currently, I am running it headless 
because I have not had the time to fix the monitor (it still has the 
framebuffer inside, but this sluggishness issue was present before with 
the monitor attached).  I have read that this can be caused by "faulty 
i/o devices that interrupt the cpu continuously".  What else can be done 
to locate the source of the problem?

Regards,

Carlos.