RELENG_7: interrupt eating whole cpu core

[Dominic Fandrey]

Dominic Fandrey wrote:
> While ripping DVDs the irq14: ata0 eats ~95% of one of my cores. The 
> channel is exclusive to the drive.
 >
 > ...
 >
> behaviour has changed. This is an HP 6510b GR695EA#ABD, if anyone thinks 
> it might be helpful, I can supply you with a dmesg and the output of 
> pciconf -lv.

The problem remains with fresh sources:

   PID USERNAME   THR PRI NICE   SIZE    RES STATE  C   TIME    CPU COMMAND
    12 root         1 171 ki31     0K    16K RUN    0  22:04 97.85% idle: cpu0
    37 root         1 -64    -     0K    16K CPU1   1   2:35 96.00% irq14: ata0
    11 root         1 171 ki31     0K    16K RUN    1  19:32  6.40% idle: cpu1

The rip is done by k3b, so the drive is accessed through the cam interface.