> But ummm.. I can't understand the author expect which effect by this volatile. > If I am correct, its volatile has no effect. we can simply remove it. It may be a legacy from when cpumask was a simple integer type. The boot cpu wakes up each "AP" cpu in turn - and spins looking at cpu_callin_mask waiting to see if the cpu has really woken up, since the AP cpu will set its own bit in this mask when it begins execution. Making the original integer mask a volatile was a way to make sure that the compiler did not optimize away the re-read of this variable in the loop. When NR_CPUS is small enough - we still use a simple integer for cpumask type - don't we? So if you remove the volatile, look very carefully at this loop: for (timeout = 0; timeout < 100000; timeout++) { if (cpu_isset(cpu, cpu_callin_map)) break; /* It has booted */ udelay(100); } to make sure that the cpu_isset() check really does look at cpu_callin_map every time (and not at some cached in a register copy of it). Booting would become painfully slow if we get stuck for 10 seconds per cpu just here. -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