Messages in this thread | | | Date | Sat, 17 Dec 2005 02:19:50 -0200 | From | Marcelo Tosatti <> | Subject | Re: [RFC3 02/14] Basic counter functionality |
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> 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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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