One thing to wonder about is whether we need to worry about SMP
systems using the processors without ll/sc (I think that the Tandem
Integrity S300 is a MP R3000 system, for example). Those systems will
hurt our heads a lot; I have to imagine that they have some extra
hardware in the interface between the CPU and the system bus that
provides locking capabilites.

However, for uniprocessor R3000 systems, we could use "restartable
sections" for moderately cheap userlevel atomicity, and we don't use
__cpu_simple_locks in the kernel on uniprocessor systems. SAs and
restartable sections have some bits in common, and I think they could
be made to work together.

I think we'd want to use the ld.so.conf/sysctl trick to select between
versions of the pthread library based on the presence of ll/sc.

        - Nathan