Linus Torvalds <[email protected]> wrote:
> The rules are, afaik, that reads can pass buffered writes, BUT WRITES
> CANNOT PASS READS (aka "writes to memory are always carried out in program
> order").
So in the example I gave, a read after the spin_unlock() may actually get
executed before the store in the spin_unlock(), but a read before the unlock
will not get executed after.
> No. Issuing a read barrier on one CPU will do absolutely _nothing_ on the
> other CPU.
Well, I think you mean will guarantee absolutely _nothing_ on the other CPU for
the Linux kernel. According to the IBM powerpc book I have, it does actually
do something on the other CPUs, though it doesn't say exactly what.
Anyway, thanks.
I'll write up some documentation on barriers for inclusion in the kernel.
David
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