Messages in this thread | | | Date | Fri, 2 Apr 2010 16:24:57 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH 4/5] kgdb: Use atomic operators which use barriers |
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On Fri, 2 Apr 2010, Russell King - ARM Linux wrote: > > Actually, in future threads you end up agreeing with my position...
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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