Messages in this thread | | | Date | Mon, 10 Sep 2007 13:54:34 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures |
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On Mon, Sep 10, 2007 at 11:59:29AM -0700, Christoph Lameter wrote: > On Fri, 17 Aug 2007, Segher Boessenkool wrote: > > > "volatile" has nothing to do with reordering. atomic_dec() writes > > to memory, so it _does_ have "volatile semantics", implicitly, as > > long as the compiler cannot optimise the atomic variable away > > completely -- any store counts as a side effect. > > Stores can be reordered. Only x86 has (mostly) implicit write ordering. So > no atomic_dec has no volatile semantics and may be reordered on a variety > of processors. Writes to memory may not follow code order on several > processors.
The one exception to this being the case where process-level code is communicating to an interrupt handler running on that same CPU -- on all CPUs that I am aware of, a given CPU always sees its own writes in order.
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