Messages in this thread | | | Date | Tue, 04 Dec 2001 19:17:45 -0800 | From | Stephen Satchell <> | Subject | Re: SMP/cc Cluster description |
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At 06:36 PM 12/4/01 -0800, David S. Miller wrote: >What is the difference between your messages and spin locks? >Both seem to shuffle between cpus anytime anything interesting >happens. > >In the spinlock case, I can thread out the locks in the page cache >hash table so that the shuffling is reduced. In the message case, I >always have to talk to someone.
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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