>> ticket = ia64_fetchadd(1, p, acq); >> >> if (!(((ticket >> TICKET_SHIFT) ^ ticket) & ((1L << TICKET_BITS) - 1))) >> return; > > I think the above is wrong. > > Doesn't 'fetchadd' return the _old_ value? Yes, It does return the old value ... but that it what we want. When we tear the ticket from the machine on the Deli counter, our ticket number is the OLD value. The updated value becomes the ticket number for the next person to come along. I.e. we start the lock with value 0x00000000, so the ticket showing is 0, and the now serving number is 0. We fetchadd a ticket and the lock goes to 0x00000001 ... and we own the lock because the ticket we pulled matches the now-serving number. When we are done we bumb the now-serving value, so the lock goes to 0x00020001 and the lock is free again. Did I do this differently from x86? -Tony -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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