rtm wrote: > Why does acquire() call cpuid()? Why does release() call cpuid()? The cpuid in acquire is redundant with the cmpxchg, as you said. I have removed the cpuid from acquire. The cpuid in release is actually doing something important, but not on the hardware. It keeps gcc from reordering the lock->locked assignment above the other two during optimization. (Not that current gcc -O2 would choose to do that, but it is allowed to.) I have replaced the cpuid in release with a "gcc barrier" that keeps gcc from moving things around but has no hardware effect. On a related note, I don't think the cpuid in mpmain is necessary, for the same reason that the cpuid wasn't needed in release. As to the question of whether acquire(); x = protected; release(); might read protected after release(), I still haven't convinced myself whether it can. I'll put the cpuid back into release if we determine that it can. Russ