On Thu, Mar 30, 2017 at 03:22:24PM +0800, Jason Wang wrote:
> This patch introduce a batched version of consuming, consumer can
> dequeue more than one pointers from the ring at a time. We don't care
> about the reorder of reading here so no need for compiler barrier.
>
> Signed-off-by: Jason Wang <jasow...@redhat.com>
> ---
> include/linux/ptr_ring.h | 65
> ++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 65 insertions(+)
>
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 6c70444..2be0f350 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -247,6 +247,22 @@ static inline void *__ptr_ring_consume(struct ptr_ring
> *r)
> return ptr;
> }
>
> +static inline int __ptr_ring_consume_batched(struct ptr_ring *r,
> + void **array, int n)
Can we use a shorter name? ptr_ring_consume_batch?
> +{
> + void *ptr;
> + int i;
> +
> + for (i = 0; i < n; i++) {
> + ptr = __ptr_ring_consume(r);
> + if (!ptr)
> + break;
> + array[i] = ptr;
> + }
> +
> + return i;
> +}
> +
> /*
> * Note: resize (below) nests producer lock within consumer lock, so if you
> * call this in interrupt or BH context, you must disable interrupts/BH when
I'd like to add a code comment here explaining why we don't
care about cpu or compiler reordering. And I think the reason is
in the way you use this API: in vhost it does not matter
if you get less entries than present in the ring.
That's ok but needs to be noted
in a code comment so people use this function correctly.
Also, I think you need to repeat the comment about cpu_relax
near this function: if someone uses it in a loop,
a compiler barrier is needed to prevent compiler from
optimizing it out.
I note that ptr_ring_consume currently lacks any of these
comments so I'm ok with merging as is, and I'll add
documentation on top.
Like this perhaps?
/* Consume up to n entries and return the number of entries consumed
* or 0 on ring empty.
* Note: this might return early with less entries than present in the
* ring.
* Note: callers invoking this in a loop must use a compiler barrier,
* for example cpu_relax(). Callers must take consumer_lock
* if the ring is ever resized - see e.g. ptr_ring_consume_batch.
*/
> @@ -297,6 +313,55 @@ static inline void *ptr_ring_consume_bh(struct ptr_ring
> *r)
> return ptr;
> }
>
> +static inline int ptr_ring_consume_batched(struct ptr_ring *r,
> + void **array, int n)
> +{
> + int ret;
> +
> + spin_lock(&r->consumer_lock);
> + ret = __ptr_ring_consume_batched(r, array, n);
> + spin_unlock(&r->consumer_lock);
> +
> + return ret;
> +}
> +
> +static inline int ptr_ring_consume_batched_irq(struct ptr_ring *r,
> + void **array, int n)
> +{
> + int ret;
> +
> + spin_lock_irq(&r->consumer_lock);
> + ret = __ptr_ring_consume_batched(r, array, n);
> + spin_unlock_irq(&r->consumer_lock);
> +
> + return ret;
> +}
> +
> +static inline int ptr_ring_consume_batched_any(struct ptr_ring *r,
> + void **array, int n)
> +{
> + unsigned long flags;
> + int ret;
> +
> + spin_lock_irqsave(&r->consumer_lock, flags);
> + ret = __ptr_ring_consume_batched(r, array, n);
> + spin_unlock_irqrestore(&r->consumer_lock, flags);
> +
> + return ret;
> +}
> +
> +static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
> + void **array, int n)
> +{
> + int ret;
> +
> + spin_lock_bh(&r->consumer_lock);
> + ret = __ptr_ring_consume_batched(r, array, n);
> + spin_unlock_bh(&r->consumer_lock);
> +
> + return ret;
> +}
> +
> /* Cast to structure type and call a function without discarding from FIFO.
> * Function must return a value.
> * Callers must take consumer_lock.
> --
> 2.7.4
