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    SubjectRe: [RFC3 02/14] Basic counter functionality

    > There is no need to disable interrupts AFAICS, but only preemption
    > (which could cause problems as your comment above describes). I suppose
    > that these counters are not accessed at interrupt time and are not meant
    > to be, right?
    > Which means that if an interrupt happens at any point in the code,
    > the state will be consistent after the IRQ(s) handler(s) finish and
    > execution restarts where it had been interrupted.
    > Why not use preempt_disable/preempt_enable? Those would disappear
    > if !CONFIG_PREEMPT, and could be faster than the interrupt
    > disabling/enabling (no need to save "flags" on stack, but increment
    > preempt count, which has a chance to be on cache, I guess).

    Which is what local_t does for BITS_PER_LONG==32 arches:

    #define LOCAL_INIT(i) { ATOMIC_INIT(i) }

    #define local_read(l) ((unsigned long)atomic_read(&(l)->a))
    #define local_set(l,i) atomic_set((&(l)->a),(i))
    #define local_inc(l) atomic_inc(&(l)->a)
    #define local_dec(l) atomic_dec(&(l)->a)
    #define local_add(i,l) atomic_add((i),(&(l)->a))
    #define local_sub(i,l) atomic_sub((i),(&(l)->a))

    /* Non-atomic variants, ie. preemption disabled and won't be touched
    * in interrupt, etc. Some archs can optimize this case well. */
    #define __local_inc(l) local_set((l), local_read(l) + 1)
    #define __local_dec(l) local_set((l), local_read(l) - 1)
    #define __local_add(i,l) local_set((l), local_read(l) + (i))
    #define __local_sub(i,l) local_set((l), local_read(l) - (i))

    > It would also be nice to have all code related to debugging only
    > counters selectable at compile time, since it might not be interesting
    > data for some scenarios (but unnecessary bloat) - seems that was the
    > original intent by Andrew as you noted.
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      Last update: 2005-12-17 05:25    [W:0.022 / U:10.360 seconds]
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