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    SubjectRe: [PATCH 0/24] make atomic_read() behave consistently across all architectures

    On Wed, 15 Aug 2007, Christoph Lameter wrote:

    > On Wed, 15 Aug 2007, Paul E. McKenney wrote:
    > > Understood. My point is not that the impact is precisely zero, but
    > > rather that the impact on optimization is much less hurtful than the
    > > problems that could arise otherwise, particularly as compilers become
    > > more aggressive in their optimizations.
    > The problems arise because barriers are not used as required. Volatile
    > has wishy washy semantics and somehow marries memory barriers with data
    > access. It is clearer to separate the two. Conceptual cleanness usually
    > translates into better code. If one really wants the volatile then lets
    > make it explicit and use
    > atomic_read_volatile()

    Completely agreed, again. To summarize again (had done so about ~100 mails
    earlier in this thread too :-) ...

    atomic_{read,set}_volatile() -- guarantees volatility also along with
    atomicity (the two _are_ different concepts after all, irrespective of
    whether callsites normally want one with the other or not)

    atomic_{read,set}_nonvolatile() -- only guarantees atomicity, compiler
    free to elid / coalesce / optimize such accesses, can keep the object
    in question cached in a local register, leads to smaller text, etc.

    As to which one should be the default atomic_read() is a question of
    whether majority of callsites (more weightage to important / hot
    codepaths, lesser to obscure callsites) want a particular behaviour.

    Do we have a consensus here? (hoping against hope, probably :-)

    [ This thread has gotten completely out of hand ... for my mail client
    alpine as well, it now seems. Reminds of that 1000+ GPLv3 fest :-) ]
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