On Wed, 11 Apr 2007 11:00:38 -0700 Zach Brown <[EMAIL PROTECTED]> wrote:
> > - /* Compensate for the ring buffer's head/tail overlap entry */ > > - nr_events += 2; /* 1 is required, 2 for good luck */ > > + /* round nr_event to next power of 2 */ > > + nr_events = roundup_pow_of_two(nr_events); > > Is that buggy? How will the code tell if head == tail means a full ring > or an empty ring? The old code added that extra event to let it tell > the ring was full before head == tail and it would think it's empty > again, I think. I'm guessing roundup(nr_events + 1) is needed. Ken uses the other (superior!) way of implementing ringbuffers: the head and tail pointers (the naming of which AIO appears to have reversed) are not constrained to the ringsize - they are simply allowed to wrap through 0xfffffff. Consequently: ring full: (head-tail == size) ring empty: head==tail numer-of-items-in-ring: head-tail add to ring: ring[head++]=item remove from ring: item=ring[tail++] (adjust the above for AIO naming assbackwardness) (requires that size be a power of 2) Many net drivers do it this way for their DMA rings. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
