Imbus/xv6-riscv-kernel
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Incorporate new understanding of/with Intel SMP spec.

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Dropped cmpxchg in favor of xchg, to match lecture notes.

Use xchg to release lock, for future protection and to
keep gcc from acting clever.
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rsc 2007-10-01 20:43:15 +00:00
parent 9fd9f80431
commit 943fd378a1
5 changed files with 25 additions and 36 deletions
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@ -102,5 +102,11 @@ after observing the earlier writes by CPU0.
So any reads in B are guaranteed to observe the
effects of writes in A.
Not sure about the second one yet.
According to the Intel manual behavior spec, the
second condition requires a serialization instruction
in release, to avoid reads in A happening after giving
up lk. No Intel SMP processor in existence actually
moves reads down after writes, but the language in
the spec allows it. There is no telling whether future
processors will need it.