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on Alpha 4100s. Basically, if you're halting or you're rebooting, you should tell all other processors to halt first. Define IPI_HALT- IPI_STOP is not what we want for this purpose, which will call prom_halt(0) on receipt. The processor running the halt or reboot wil send an IPI_HALT to all other processors, delay a bit, then continue to do what what it was planning on doing (prom_halt({0|1})).