Because the IDE layer disables the shared IRQ in question for periods of
time of you dont have hdparm -u set, and for some periods of time anyway.
Basically its the IDE code being obnoxious. Fixing the IDE locking would
improve this, but would be a real pain because older IDE controllers you
want to disable_irq and stuff to avoid nasty performance problems.
Actually, it's worse than that. On some older IDE controllers not
turning off interrupts will cause data corruption on the disk. Read the
hdparm man page about the -u option..... If it were only performance
problems, given that it screws over the serial driver, we could make the
argument to change the default. But given that on some trashy hardware
it causes data loss, it's harder to make that argument.... or I would
have made it a long time ago. (hdparm -u should be in the serial HOWTO
and a number of FAQ's, though!)
- Ted
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