On Fri, 2 Apr 2010, Russell King - ARM Linux wrote:
I always agreed that it was not a memory barrier.
In fact, the commit that extended on the "volatile-considered-harmful"
patch from you has this quote from me in the commit logs:
Linus sayeth:
: I don't think it was ever the intention that it would be seen as anything
: but a compiler barrier, although it is obviously implied that it might
: well perform some per-architecture actions that have "memory barrier-like"
: semantics.
:
: After all, the whole and only point of the "cpu_relax()" thing is to tell
: the CPU that we're busy-looping on some event.
:
: And that "event" might be (and often is) about reading the same memory
: location over and over until it changes to what we want it to be. So it's
: quite possible that on various architectures the "cpu_relax()" could be
: about making sure that such a tight loop on loads doesn't starve cache
: transactions, for example - and as such look a bit like a memory barrier
: from a CPU standpoint.
:
: But it's not meant to have any kind of architectural memory ordering
: semantics as far as the kernel is concerned - those must come from other
: sources.
which I think is pretty clear.
But that quote seems to be the one where you then think I "agree" with
you.
Linus
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