While what I'm about to say has little bearing on the SMP/cc case: one
significant advantage of messages over spinlocks is being able to assign
priority with low overhead in the quick-response real-time multi-CPU
arena. I worked with a cluster of up to 14 CPUs using something very much
like NUMA in which task scheduling used a set of prioritized message
queues. The system I worked on was designed to break transaction-oriented
tasks into a string of "work units" each of which could be processed very
quickly -- on the order of three milliseconds or less. (The limit of 14
CPUs was set by the hardware used to implement the main system bus.)
I bring this up only because I have never seen a spinlock system that dealt
with priority issues very well when under heavy load.
OK, I've said my piece, now I'll sit back and continue to watch your
discussion.
Satch
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