DragonFly kernel List (threaded) for 2006-11
Re: splxxx replacements?
:Thanks for some explanation. However, it seems the crit_enter/exit only
:works on one CPU in an SMP environment too (looking back at previous
:posting in thread). Is there really a practical as well as conceptual
There are several differences.
* The crit*() calls can nest. The spl*() calls were able to nest, but
there was no nesting count tracking so if code screwed up the nesting
(forgot a splx() for example) the whole system could get confused.
* spl*() calls imply a limited number of interrupt sources. 32 in our
case. I don't want that abstraction to be visible to machine
* The code generated to handle the crit*() calls is a lot less cumbersome
then the code generated to handle the spl*() calls.
* For any modern device, interrupt overhead is in the low microseconds
range and the interrupt is not typically time-sensitive the way
a serial interrupt is. Interrupting an interrupt is really
* A multi-layer abstraction (where one interrupt can interrupt another
interrupt)... also known as preemption in FreeBSDland, is a bad idea
that can lead to all sorts of unexpected side effects. I just don't
want to have to deal with it.