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    SubjectRe: local_add_return
    On Tuesday 23 December 2008 05:13:28 Mathieu Desnoyers wrote:
    > > I can be convinced, but I'll need more than speculation. Assuming
    > > local_long_atomic_t, can you produce a patch which uses it somewhere else?
    > I had this patch applying over Christoph Lameter's vm tree last
    > February. It did accelerate the slub fastpath allocator by using
    > cmpxchg_local rather than disabling interrupts. cmpxchg_local is not
    > using the local_t type, but behaves similarly to local_cmpxchg.

    OK, I'll buy that. So we split local_t into a counter and an atomic type.

    > I know that
    > local_counter_long_t and local_atomic_long_t are painful to write, but
    > that would follow the current atomic_t vs atomic_long_t semantics. Hm ?

    OK, I've looked at how they're used, to try to figure out whether long
    is the right thing. Counters generally want to be long, but I was in doubt
    about atomics; yet grep shows that atomic_long_t is quite popular. Then
    I hit struct nfs_iostats which would want a u64 and a long. I don't think
    we want local_counter_u64 etc.

    Just thinking out loud, perhaps a new *type* is the wrong direction? How
    about a set of macros which take a fundamental type, such as:

    DECLARE_LOCAL_COUNTER(type, name);
    local_counter_inc(type, addr);
    DECLARE_LOCAL_ATOMIC(type, name);
    local_atomic_add_return(type, addr);

    This allows pointers, u32, u64, long, etc. If a 32-bit arch can't do 64-bit
    local_counter_inc easily, at least the hairy 64-bit code can be eliminated at
    compile time.

    Or maybe that's overdesign?

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      Last update: 2008-12-24 12:45    [W:0.019 / U:11.756 seconds]
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