On Thu, Oct 04, 2018 at 10:40:55PM -0500, Mauricio Vasquez wrote: > > > > + /* Round up queue size to nearest power of 2 */ > > > + max_entries = index_mask + 1; > > what's the point of roundup ? > > If the size of the buffer is power of two we can wrap the indexes with an > AND operation instead of MOD. > > > The memory waste becomes quite large when max_entries are high. > Yes, you are right, we have the different choices described below. > > > > > If queue/stack is sized to exact max_entries, > > then 'count' can be removed too, right? > > If we don't use 'count' and we want to use the AND operation for wrapping > indexes, the max entries should be 2^ - 1 because a slot is lost to > distinguish between full/empty queue/stack. > > Just to summarize, we have these options: > 1. Allow any size, round up, use the AND operation and 'count' (current). > 2. Allow only power of 2 sizes, use the AND operation and 'count'. > 3. Allow any size, no roundup, use the MOD operation and leaving an empty > slot. > > I prefer 1 or 2, but I don't have a strong opinion, maybe allowing only > power of two max entries could be too limiting. > Another consideration: is this really too bad to waste memory when user > requires a size far away of the next power of 2?
I think there is 4th option. Neither AND nor MOD is necessary. Pls take a look at ptr_ring implementation.
