> >	- obsolete IPLs.
> >	  (like freebsd.  i think my old patch contains an equivalent hack.)
> 
> Yes; your old patch for i386 SMP effectively collapsed all SPLs to a
> single level. That way, no driver should interrupt another.

Make careful measurements as to how this impacts interrupt latency.
Having the serial driver interrupt the audio driver to process
characters is a good thing (16550's have a much lower latency
tolerance than do most audio devices).  If too much of the kernel
blocks interrupts entirely, this can create starvation for things like
16550 RX FIFOs.

Warner