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    SubjectMemory-ordering recipes
    Hello!

    The topic of memory-ordering recipes came up at the Linux Plumbers
    Conference microconference on Friday, so I thought that I should summarize
    what is currently "out there":

    1. memory-barriers.txt: A bit rambling and diffuse for a recipes
    document.

    2. https://www.kernel.org/pub/linux/kernel/people/paulmck/LWNLinuxMM/Examples.html
    Many of the examples are on-point, but this is aimed more
    at understanding the memory model than at an organized set
    of recipes.

    3. https://www.kernel.org/pub/linux/kernel/people/paulmck/LWNLinuxMM/Examples.html
    Slides 15-20. Again, some of the litmus tests are on-point,
    but the focus is more on understanding the memory model than on
    an organized set of recipes.

    So what litmus tests are needed? Here is my initial set:

    1. Release-acquire chains, AKA ISA2, Z6.2, LB, and 3.LB

    Lots of variety here, can in some cases substitute:

    a. READ_ONCE() for smp_load_acquire()
    b. WRITE_ONCE() for smp_store_release()
    c. Dependencies for both smp_load_acquire() and
    smp_store_release().
    d. smp_wmb() for smp_store_release() in first thread
    of ISA2 and Z6.2.
    e. smp_rmb() for smp_load_acquire() in last thread of ISA2.

    2. MP (see test6.pdf for nickname translation)

    a. smp_store_release() / smp_load_acquire()
    b. rcu_assign_pointer() / rcu_dereference()
    c. smp_wmb() / smp_rmb()
    d. Replacing either of the above with smp_mb()

    3. SB

    a. smp_mb(), as in lockless wait-wakeup coordination.
    And as in sys_membarrier()-scheduler coordination,
    for that matter.

    Others?

    Thanx, Paul

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