On Tue, Jul 29, 2014 at 2:10 PM, Nathan Hjelm <hje...@lanl.gov> wrote:
> Is there a reason why the > current implementations of opal atomics (add, cmpset) do not return the > old value? > Because some CPUs don't implement such an atomic instruction? On any CPU one *can* certainly synthesize the desired operation with an added read before the compare-and-swap to return a value that was present at some time before a failed cmpset. That is almost certainly sufficient for your purposes. However, the added load makes it (marginally) more expensive on some CPUs that only have the native equivalent of gcc's __sync_bool_compare_and_swap(). -Paul -- Paul H. Hargrove phhargr...@lbl.gov Future Technologies Group Computer and Data Sciences Department Tel: +1-510-495-2352 Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
