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    SubjectRe: [PATCH] Profile likely/unlikely macros
    On Wed, 26 April 2006 11:08:09 +1000, Nick Piggin wrote:
    > Daniel Walker wrote:
    >
    > Ah, I see. Then you should be OK with either your current scheme, or
    > Andrew's suggestion, so long as you have a memory barrier before the
    > unlock (eg. smp_mb__before_clear_bit()).
    >
    > >I'm not exactly sure what you mean by "release consistency" ?
    >
    > Without a barrier, the stores to the linked list may be visible to another
    > CPU after the store that unlocks the atomic_t. Ie. the critical section can
    > leak out of the lock.

    Admitted, I'm a bit slow at times. But why does this matter?
    According to my fairly limited brain, you take a potentially expensive
    barrier, so you pay with a bit of runtime. What you buy is a smaller
    critical section, so you can save some runtime on other cpus. When
    optimizing for the common case, which is one cpu, this is a net loss.

    There must be some correctness issue hidden that I cannot see. Can
    you explain that to me?

    Jörn

    --
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    -- Sun Tzu
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