Hi Andrzej,
On Mon, Jan 03, 2022 at 03:22:01PM +0100, Andrzej Ostruszka wrote:
> ring: fix off by 1 mistake
I suggest something less scary for the title:
ring: optimize corner case for enqueue/dequeue
> When enqueueing/dequeueing to/from the ring we try to optimize by manual
> loop unrolling. The check for this optimization looks like:
>
> if (likely(idx + n < size)) {
>
> where 'idx' points to the first usable element (empty slot for enqueue,
> data for dequeue). The correct comparison here should be '<=' instead
> of '<'.
>
> This is not a functional error since we fall back to the loop with
> correct checks on indexes. Just a minor suboptimal behaviour for the
> case when we want to enqueue/dequeue exactly the number of elements that
> we have in the ring before wrapping to its beginning.
>
> Signed-off-by: Andrzej Ostruszka <[email protected]>
Reviewed-by: Olivier Matz <[email protected]>
I'll tend to add:
Fixes: cc4b218790f6 ("ring: support configurable element size")
But the same error was in the ENQUEUE_PTRS()/DEQUEUE_PTRS() macros
since the beginning, so we may also add:
Fixes: 286bd05bf70d ("ring: optimisations")
This macro was removed in commit 2d6ed071a8b9 ("ring: use custom element
for fixed size API")
Thanks!
