On Fri, 2002-03-15 at 11:11, Mikael Pettersson wrote:
> "more than likely": that's perhaps true for your average NIC/soundcard/
> whatever driver, but things that poke the processor itself (like my
> performance-monitoring counters driver) really do depend on not being
> preempted. In my view, CONFIG_SMP is a minor triviality compared to
> CONFIG_PREEMPT ...
If you "poke the processor", to be SMP-safe, you should hold a lock to
prevent multiple concurrent "pokings of the processor" - thus you become
preempt-safe.
It is a rare case where something does not hold lock, assumes some sort
of non-reentrancy/concurrency, and is actually still SMP-safe. The only
nontrivial case I have seen is drivers that call disable_irq(n) and thus
are assured they won't have another driver request and then go off to
touch hardware.
In general, the sort of "non-preemptibility" you are requiring is also a
requirement for non-reentrancy and non-concurrency and thus your
measures to protect those (SMP locking, et al) assure you your
preempt-kernel protection, too.
Robert Love
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This archive was generated by hypermail 2b29 : Fri Mar 15 2002 - 22:00:21 EST