* you (speculatively) execute read instructions ahead of write
instructions.
* you do not send write instructions immediately out of the CPU core,
they sit in a write buffer.
* the write buffer is private to each CPU.
* on _single_ cpu, you correct the effects of the reordering (ie if a
write sits in the write buffer, and I reread that memory address, the
the CPU notices that, and uses the new value from the write
buffer/discards the temporary result.)
BUT: since the write buffer is private to each CPU, you cannot correct
the effects of the reordering on SMP.
The program that I sent you yesterday exploits this problem, you could
run it with a suitable tracer:
* with "lock;bts", it doesn't hang.
* with "mov", it hangs.
-- Manfred
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