Re: [PATCH net-next 1/8] ptr_ring: introduce batch dequeuing

[Jason Wang]

On 2017年03月22日 21:43, Michael S. Tsirkin wrote:
On Tue, Mar 21, 2017 at 12:04:40PM +0800, Jason Wang wrote:
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..4771ded 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)
+{
+       void *ptr;
+       int i = 0;
+
+       while (i < n) {
+               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

This ignores the comment above that function:

/* Note: callers invoking this in a loop must use a compiler barrier,
  * for example cpu_relax().
  */

Yes, __ptr_ring_swap_queue() ignores this too.


Also - it looks like it shouldn't matter if reads are reordered but I wonder.
Thoughts? Including some reasoning about it in commit log would be nice.

Yes, I think it doesn't matter in this case, it matters only for batched 
producing.

Thanks


@@ -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